diff --git a/core/app/models/concerns/spree/user_address_book.rb b/core/app/models/concerns/spree/user_address_book.rb
index eb543036c35..466dbd826b9 100644
--- a/core/app/models/concerns/spree/user_address_book.rb
+++ b/core/app/models/concerns/spree/user_address_book.rb
@@ -25,7 +25,7 @@ def mark_default(user_address)
       has_many :addresses, through: :user_addresses
 
       # bill_address is only minimally used now, but we can't get rid of it without a major version release
-      belongs_to :bill_address, class_name: 'Spree::Address'
+      belongs_to :bill_address, class_name: 'Spree::Address', optional: true
 
       has_one :default_user_address, ->{ default }, class_name: 'Spree::UserAddress', foreign_key: 'user_id'
       has_one :default_address, through: :default_user_address, source: :address
diff --git a/core/app/models/spree/address.rb b/core/app/models/spree/address.rb
index aec76e284e2..6513997f068 100644
--- a/core/app/models/spree/address.rb
+++ b/core/app/models/spree/address.rb
@@ -8,8 +8,8 @@ module Spree
   class Address < Spree::Base
     extend ActiveModel::ForbiddenAttributesProtection
 
-    belongs_to :country, class_name: "Spree::Country"
-    belongs_to :state, class_name: "Spree::State"
+    belongs_to :country, class_name: "Spree::Country", optional: true
+    belongs_to :state, class_name: "Spree::State", optional: true
 
     validates :firstname, :address1, :city, :country_id, presence: true
     validates :zipcode, presence: true, if: :require_zipcode?
diff --git a/core/app/models/spree/adjustment.rb b/core/app/models/spree/adjustment.rb
index 8f16c80fc72..2425ed19b38 100644
--- a/core/app/models/spree/adjustment.rb
+++ b/core/app/models/spree/adjustment.rb
@@ -16,11 +16,11 @@ module Spree
   #    order's adjustment total. This allows an adjustment to be preserved if
   #    it becomes ineligible so it might be reinstated.
   class Adjustment < Spree::Base
-    belongs_to :adjustable, polymorphic: true, touch: true
-    belongs_to :source, polymorphic: true
-    belongs_to :order, class_name: 'Spree::Order', inverse_of: :all_adjustments
-    belongs_to :promotion_code, class_name: 'Spree::PromotionCode'
-    belongs_to :adjustment_reason, class_name: 'Spree::AdjustmentReason', inverse_of: :adjustments
+    belongs_to :adjustable, polymorphic: true, touch: true, optional: true
+    belongs_to :source, polymorphic: true, optional: true
+    belongs_to :order, class_name: 'Spree::Order', inverse_of: :all_adjustments, optional: true
+    belongs_to :promotion_code, class_name: 'Spree::PromotionCode', optional: true
+    belongs_to :adjustment_reason, class_name: 'Spree::AdjustmentReason', inverse_of: :adjustments, optional: true
 
     validates :adjustable, presence: true
     validates :order, presence: true
diff --git a/core/app/models/spree/asset.rb b/core/app/models/spree/asset.rb
index 27ea73ac218..aed2412478f 100644
--- a/core/app/models/spree/asset.rb
+++ b/core/app/models/spree/asset.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class Asset < Spree::Base
-    belongs_to :viewable, polymorphic: true, touch: true
+    belongs_to :viewable, polymorphic: true, touch: true, optional: true
     acts_as_list scope: [:viewable_id, :viewable_type]
   end
 end
diff --git a/core/app/models/spree/calculator.rb b/core/app/models/spree/calculator.rb
index 0bec110dcb1..2773570b1b7 100644
--- a/core/app/models/spree/calculator.rb
+++ b/core/app/models/spree/calculator.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class Calculator < Spree::Base
-    belongs_to :calculable, polymorphic: true
+    belongs_to :calculable, polymorphic: true, optional: true
 
     # This method calls a compute_<computable> method. must be overriden in concrete calculator.
     #
diff --git a/core/app/models/spree/carton.rb b/core/app/models/spree/carton.rb
index 444d7080dff..931b3b62dff 100644
--- a/core/app/models/spree/carton.rb
+++ b/core/app/models/spree/carton.rb
@@ -1,9 +1,9 @@
 # frozen_string_literal: true
 
 class Spree::Carton < Spree::Base
-  belongs_to :address, class_name: 'Spree::Address'
-  belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :cartons
-  belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', inverse_of: :cartons
+  belongs_to :address, class_name: 'Spree::Address', optional: true
+  belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :cartons, optional: true
+  belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', inverse_of: :cartons, optional: true
 
   has_many :inventory_units, class_name: "Spree::InventoryUnit", inverse_of: :carton, dependent: :nullify
   has_many :orders, -> { distinct }, through: :inventory_units
diff --git a/core/app/models/spree/classification.rb b/core/app/models/spree/classification.rb
index 8a4446c181d..4966625014a 100644
--- a/core/app/models/spree/classification.rb
+++ b/core/app/models/spree/classification.rb
@@ -4,8 +4,8 @@ module Spree
   class Classification < Spree::Base
     self.table_name = 'spree_products_taxons'
     acts_as_list scope: :taxon
-    belongs_to :product, class_name: "Spree::Product", inverse_of: :classifications, touch: true
-    belongs_to :taxon, class_name: "Spree::Taxon", inverse_of: :classifications, touch: true
+    belongs_to :product, class_name: "Spree::Product", inverse_of: :classifications, touch: true, optional: true
+    belongs_to :taxon, class_name: "Spree::Taxon", inverse_of: :classifications, touch: true, optional: true
 
     # For https://github.com/spree/spree/issues/3494
     validates_uniqueness_of :taxon_id, scope: :product_id, message: :already_linked
diff --git a/core/app/models/spree/credit_card.rb b/core/app/models/spree/credit_card.rb
index be71ae57dca..c3f6362b8ae 100644
--- a/core/app/models/spree/credit_card.rb
+++ b/core/app/models/spree/credit_card.rb
@@ -4,8 +4,8 @@ module Spree
   # The default `source` of a `Spree::Payment`.
   #
   class CreditCard < Spree::PaymentSource
-    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id'
-    belongs_to :address
+    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', optional: true
+    belongs_to :address, optional: true
 
     before_save :set_last_digits
 
diff --git a/core/app/models/spree/customer_return.rb b/core/app/models/spree/customer_return.rb
index de9276b618a..6062b06008a 100644
--- a/core/app/models/spree/customer_return.rb
+++ b/core/app/models/spree/customer_return.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class CustomerReturn < Spree::Base
-    belongs_to :stock_location
+    belongs_to :stock_location, optional: true
 
     has_many :return_items, inverse_of: :customer_return
     has_many :return_authorizations, through: :return_items
diff --git a/core/app/models/spree/inventory_unit.rb b/core/app/models/spree/inventory_unit.rb
index 14e677b076a..34f51dcd3de 100644
--- a/core/app/models/spree/inventory_unit.rb
+++ b/core/app/models/spree/inventory_unit.rb
@@ -8,10 +8,10 @@ class InventoryUnit < Spree::Base
     POST_SHIPMENT_STATES = %w(returned)
     CANCELABLE_STATES = ['on_hand', 'backordered', 'shipped']
 
-    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :inventory_units
-    belongs_to :shipment, class_name: "Spree::Shipment", touch: true, inverse_of: :inventory_units
-    belongs_to :carton, class_name: "Spree::Carton", inverse_of: :inventory_units
-    belongs_to :line_item, class_name: "Spree::LineItem", inverse_of: :inventory_units
+    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :inventory_units, optional: true
+    belongs_to :shipment, class_name: "Spree::Shipment", touch: true, inverse_of: :inventory_units, optional: true
+    belongs_to :carton, class_name: "Spree::Carton", inverse_of: :inventory_units, optional: true
+    belongs_to :line_item, class_name: "Spree::LineItem", inverse_of: :inventory_units, optional: true
 
     has_many :return_items, inverse_of: :inventory_unit, dependent: :destroy
     has_one :original_return_item, class_name: "Spree::ReturnItem", foreign_key: :exchange_inventory_unit_id, dependent: :destroy
diff --git a/core/app/models/spree/line_item.rb b/core/app/models/spree/line_item.rb
index 5181e9a5464..79e24863319 100644
--- a/core/app/models/spree/line_item.rb
+++ b/core/app/models/spree/line_item.rb
@@ -12,9 +12,9 @@ module Spree
   class LineItem < Spree::Base
     class CurrencyMismatch < StandardError; end
 
-    belongs_to :order, class_name: "Spree::Order", inverse_of: :line_items, touch: true
-    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :line_items
-    belongs_to :tax_category, class_name: "Spree::TaxCategory"
+    belongs_to :order, class_name: "Spree::Order", inverse_of: :line_items, touch: true, optional: true
+    belongs_to :variant, -> { with_deleted }, class_name: "Spree::Variant", inverse_of: :line_items, optional: true
+    belongs_to :tax_category, class_name: "Spree::TaxCategory", optional: true
 
     has_one :product, through: :variant
 
diff --git a/core/app/models/spree/line_item_action.rb b/core/app/models/spree/line_item_action.rb
index 4d84bb0a13a..aa280298cf0 100644
--- a/core/app/models/spree/line_item_action.rb
+++ b/core/app/models/spree/line_item_action.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class LineItemAction < Spree::Base
-    belongs_to :line_item
-    belongs_to :action, class_name: "Spree::PromotionAction"
+    belongs_to :line_item, optional: true
+    belongs_to :action, class_name: "Spree::PromotionAction", optional: true
   end
 end
diff --git a/core/app/models/spree/log_entry.rb b/core/app/models/spree/log_entry.rb
index bd9ce217c8a..2e3bd32a456 100644
--- a/core/app/models/spree/log_entry.rb
+++ b/core/app/models/spree/log_entry.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class LogEntry < Spree::Base
-    belongs_to :source, polymorphic: true
+    belongs_to :source, polymorphic: true, optional: true
 
     def parsed_details
       @details ||= YAML.load(details)
diff --git a/core/app/models/spree/option_value.rb b/core/app/models/spree/option_value.rb
index 99e8577dc22..a0b79252b9a 100644
--- a/core/app/models/spree/option_value.rb
+++ b/core/app/models/spree/option_value.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class OptionValue < Spree::Base
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :option_values, optional: true
     acts_as_list scope: :option_type
 
     has_many :option_values_variants, dependent: :destroy
diff --git a/core/app/models/spree/option_values_variant.rb b/core/app/models/spree/option_values_variant.rb
index 18d4766ec9d..58742f54b46 100644
--- a/core/app/models/spree/option_values_variant.rb
+++ b/core/app/models/spree/option_values_variant.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class OptionValuesVariant < Spree::Base
-    belongs_to :variant
-    belongs_to :option_value
+    belongs_to :variant, optional: true
+    belongs_to :option_value, optional: true
   end
 end
diff --git a/core/app/models/spree/order.rb b/core/app/models/spree/order.rb
index bde803c1d48..719e348581f 100644
--- a/core/app/models/spree/order.rb
+++ b/core/app/models/spree/order.rb
@@ -55,15 +55,15 @@ class CannotRebuildShipments < StandardError; end
     deprecate :temporary_credit_card= => :temporary_payment_source=, deprecator: Spree::Deprecation
 
     # Customer info
-    belongs_to :user, class_name: Spree::UserClassHandle.new
-    belongs_to :bill_address, foreign_key: :bill_address_id, class_name: 'Spree::Address'
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :bill_address, foreign_key: :bill_address_id, class_name: 'Spree::Address', optional: true
     alias_attribute :billing_address, :bill_address
 
-    belongs_to :ship_address, foreign_key: :ship_address_id, class_name: 'Spree::Address'
+    belongs_to :ship_address, foreign_key: :ship_address_id, class_name: 'Spree::Address', optional: true
     alias_attribute :shipping_address, :ship_address
     alias_attribute :ship_total, :shipment_total
 
-    belongs_to :store, class_name: 'Spree::Store'
+    belongs_to :store, class_name: 'Spree::Store', optional: true
 
     # Items
     has_many :line_items, -> { order(:created_at, :id) }, dependent: :destroy, inverse_of: :order
@@ -101,9 +101,9 @@ def states
 
     # Logging
     has_many :state_changes, as: :stateful
-    belongs_to :created_by, class_name: Spree::UserClassHandle.new
-    belongs_to :approver, class_name: Spree::UserClassHandle.new
-    belongs_to :canceler, class_name: Spree::UserClassHandle.new
+    belongs_to :created_by, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :approver, class_name: Spree::UserClassHandle.new, optional: true
+    belongs_to :canceler, class_name: Spree::UserClassHandle.new, optional: true
 
     accepts_nested_attributes_for :line_items
     accepts_nested_attributes_for :bill_address
diff --git a/core/app/models/spree/order_mutex.rb b/core/app/models/spree/order_mutex.rb
index 503ceb7092f..4fca9fd193a 100644
--- a/core/app/models/spree/order_mutex.rb
+++ b/core/app/models/spree/order_mutex.rb
@@ -4,7 +4,7 @@ module Spree
   class OrderMutex < Spree::Base
     class LockFailed < StandardError; end
 
-    belongs_to :order, class_name: "Spree::Order"
+    belongs_to :order, class_name: "Spree::Order", optional: true
 
     scope :expired, -> { where(arel_table[:created_at].lteq(Spree::Config[:order_mutex_max_age].seconds.ago)) }
 
diff --git a/core/app/models/spree/order_promotion.rb b/core/app/models/spree/order_promotion.rb
index 07450fa9598..b2a5464c2fc 100644
--- a/core/app/models/spree/order_promotion.rb
+++ b/core/app/models/spree/order_promotion.rb
@@ -8,9 +8,9 @@ module Spree
   class OrderPromotion < Spree::Base
     self.table_name = 'spree_orders_promotions'
 
-    belongs_to :order, class_name: 'Spree::Order'
-    belongs_to :promotion, class_name: 'Spree::Promotion'
-    belongs_to :promotion_code, class_name: 'Spree::PromotionCode'
+    belongs_to :order, class_name: 'Spree::Order', optional: true
+    belongs_to :promotion, class_name: 'Spree::Promotion', optional: true
+    belongs_to :promotion_code, class_name: 'Spree::PromotionCode', optional: true
 
     validates :order, presence: true
     validates :promotion, presence: true
diff --git a/core/app/models/spree/payment.rb b/core/app/models/spree/payment.rb
index d9889db7517..701c83cdf17 100644
--- a/core/app/models/spree/payment.rb
+++ b/core/app/models/spree/payment.rb
@@ -15,9 +15,9 @@ class Payment < Spree::Base
     NON_RISKY_AVS_CODES = ['B', 'D', 'H', 'J', 'M', 'Q', 'T', 'V', 'X', 'Y'].freeze
     RISKY_AVS_CODES     = ['A', 'C', 'E', 'F', 'G', 'I', 'K', 'L', 'N', 'O', 'P', 'R', 'S', 'U', 'W', 'Z'].freeze
 
-    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :payments
-    belongs_to :source, polymorphic: true
-    belongs_to :payment_method, -> { with_deleted }, class_name: 'Spree::PaymentMethod', inverse_of: :payments
+    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :payments, optional: true
+    belongs_to :source, polymorphic: true, optional: true
+    belongs_to :payment_method, -> { with_deleted }, class_name: 'Spree::PaymentMethod', inverse_of: :payments, optional: true
 
     has_many :offsets, -> { offset_payment }, class_name: "Spree::Payment", foreign_key: :source_id
     has_many :log_entries, as: :source
diff --git a/core/app/models/spree/payment_capture_event.rb b/core/app/models/spree/payment_capture_event.rb
index c137c345420..b6fcb143edc 100644
--- a/core/app/models/spree/payment_capture_event.rb
+++ b/core/app/models/spree/payment_capture_event.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PaymentCaptureEvent < Spree::Base
-    belongs_to :payment, class_name: 'Spree::Payment'
+    belongs_to :payment, class_name: 'Spree::Payment', optional: true
 
     def display_amount
       Spree::Money.new(amount, { currency: payment.currency })
diff --git a/core/app/models/spree/payment_source.rb b/core/app/models/spree/payment_source.rb
index f7ab8590d3a..91b17cc77c6 100644
--- a/core/app/models/spree/payment_source.rb
+++ b/core/app/models/spree/payment_source.rb
@@ -4,7 +4,7 @@ module Spree
   class PaymentSource < Spree::Base
     self.abstract_class = true
 
-    belongs_to :payment_method
+    belongs_to :payment_method, optional: true
 
     has_many :payments, as: :source
     has_many :wallet_payment_sources, class_name: 'Spree::WalletPaymentSource', as: :payment_source, inverse_of: :payment_source
diff --git a/core/app/models/spree/price.rb b/core/app/models/spree/price.rb
index 7b60356dcc4..198b6ac7943 100644
--- a/core/app/models/spree/price.rb
+++ b/core/app/models/spree/price.rb
@@ -12,8 +12,8 @@ class Price < Spree::Base
 
     MAXIMUM_AMOUNT = BigDecimal('99_999_999.99')
 
-    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', touch: true
-    belongs_to :country, class_name: "Spree::Country", foreign_key: "country_iso", primary_key: "iso"
+    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', touch: true, optional: true
+    belongs_to :country, class_name: "Spree::Country", foreign_key: "country_iso", primary_key: "iso", optional: true
 
     delegate :product, to: :variant
     delegate :tax_rates, to: :variant
diff --git a/core/app/models/spree/product.rb b/core/app/models/spree/product.rb
index 907c63436cf..04d0ddb34fa 100644
--- a/core/app/models/spree/product.rb
+++ b/core/app/models/spree/product.rb
@@ -44,8 +44,8 @@ class Product < Spree::Base
     has_many :product_promotion_rules, dependent: :destroy
     has_many :promotion_rules, through: :product_promotion_rules
 
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory'
-    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :products
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', optional: true
+    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :products, optional: true
 
     has_one :master,
       -> { where(is_master: true).with_deleted },
diff --git a/core/app/models/spree/product_option_type.rb b/core/app/models/spree/product_option_type.rb
index 4c0f398ea7a..cf1f7704dbc 100644
--- a/core/app/models/spree/product_option_type.rb
+++ b/core/app/models/spree/product_option_type.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class ProductOptionType < Spree::Base
-    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types
+    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true, optional: true
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types, optional: true
     acts_as_list scope: :product
   end
 end
diff --git a/core/app/models/spree/product_promotion_rule.rb b/core/app/models/spree/product_promotion_rule.rb
index 98a29893e30..c12df3f4be9 100644
--- a/core/app/models/spree/product_promotion_rule.rb
+++ b/core/app/models/spree/product_promotion_rule.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ProductPromotionRule < Spree::Base
-    belongs_to :product
-    belongs_to :promotion_rule
+    belongs_to :product, optional: true
+    belongs_to :promotion_rule, optional: true
   end
 end
diff --git a/core/app/models/spree/product_property.rb b/core/app/models/spree/product_property.rb
index 6e0c383ab12..a5f91b719e6 100644
--- a/core/app/models/spree/product_property.rb
+++ b/core/app/models/spree/product_property.rb
@@ -6,8 +6,8 @@ class ProductProperty < Spree::Base
 
     acts_as_list scope: :product
 
-    belongs_to :product, touch: true, class_name: 'Spree::Product', inverse_of: :product_properties
-    belongs_to :property, class_name: 'Spree::Property', inverse_of: :product_properties
+    belongs_to :product, touch: true, class_name: 'Spree::Product', inverse_of: :product_properties, optional: true
+    belongs_to :property, class_name: 'Spree::Property', inverse_of: :product_properties, optional: true
 
     self.whitelisted_ransackable_attributes = ['value']
   end
diff --git a/core/app/models/spree/promotion.rb b/core/app/models/spree/promotion.rb
index 47beaf010d0..bccc75b75c8 100644
--- a/core/app/models/spree/promotion.rb
+++ b/core/app/models/spree/promotion.rb
@@ -7,7 +7,7 @@ class Promotion < Spree::Base
 
     attr_reader :eligibility_errors
 
-    belongs_to :promotion_category
+    belongs_to :promotion_category, optional: true
 
     has_many :promotion_rules, autosave: true, dependent: :destroy, inverse_of: :promotion
     alias_method :rules, :promotion_rules
diff --git a/core/app/models/spree/promotion_action.rb b/core/app/models/spree/promotion_action.rb
index 25519060baa..e40262f678c 100644
--- a/core/app/models/spree/promotion_action.rb
+++ b/core/app/models/spree/promotion_action.rb
@@ -14,7 +14,7 @@ class PromotionAction < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_actions
+    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_actions, optional: true
 
     scope :of_type, ->(t) { where(type: Array.wrap(t).map(&:to_s)) }
     scope :shipping, -> { of_type(Spree::Config.environment.promotions.shipping_actions.to_a) }
diff --git a/core/app/models/spree/promotion_code.rb b/core/app/models/spree/promotion_code.rb
index 8fc72ee7fe4..215c71d8f8c 100644
--- a/core/app/models/spree/promotion_code.rb
+++ b/core/app/models/spree/promotion_code.rb
@@ -1,8 +1,8 @@
 # frozen_string_literal: true
 
 class Spree::PromotionCode < Spree::Base
-  belongs_to :promotion, inverse_of: :codes
-  belongs_to :promotion_code_batch, class_name: "Spree::PromotionCodeBatch"
+  belongs_to :promotion, inverse_of: :codes, optional: true
+  belongs_to :promotion_code_batch, class_name: "Spree::PromotionCodeBatch", optional: true
   has_many :adjustments
 
   validates :value, presence: true, uniqueness: { allow_blank: true }
diff --git a/core/app/models/spree/promotion_code_batch.rb b/core/app/models/spree/promotion_code_batch.rb
index 755a9ba0436..699885164cc 100644
--- a/core/app/models/spree/promotion_code_batch.rb
+++ b/core/app/models/spree/promotion_code_batch.rb
@@ -5,7 +5,7 @@ class PromotionCodeBatch < ActiveRecord::Base
     class CantProcessStartedBatch < StandardError
     end
 
-    belongs_to :promotion, class_name: "Spree::Promotion"
+    belongs_to :promotion, class_name: "Spree::Promotion", optional: true
     has_many :promotion_codes, class_name: "Spree::PromotionCode", dependent: :destroy
 
     validates :number_of_codes, numericality: { greater_than: 0 }
diff --git a/core/app/models/spree/promotion_rule.rb b/core/app/models/spree/promotion_rule.rb
index bbc2b67f1c3..22791d9f471 100644
--- a/core/app/models/spree/promotion_rule.rb
+++ b/core/app/models/spree/promotion_rule.rb
@@ -3,7 +3,7 @@
 module Spree
   # Base class for all promotion rules
   class PromotionRule < Spree::Base
-    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_rules
+    belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_rules, optional: true
 
     scope :of_type, ->(t) { where(type: t) }
 
diff --git a/core/app/models/spree/promotion_rule_role.rb b/core/app/models/spree/promotion_rule_role.rb
index 2d9243438c8..f6dc3b7a022 100644
--- a/core/app/models/spree/promotion_rule_role.rb
+++ b/core/app/models/spree/promotion_rule_role.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PromotionRuleRole < ActiveRecord::Base
-    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule'
-    belongs_to :role, class_name: 'Spree::Role'
+    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule', optional: true
+    belongs_to :role, class_name: 'Spree::Role', optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_store.rb b/core/app/models/spree/promotion_rule_store.rb
index db013de164b..d0456cd728c 100644
--- a/core/app/models/spree/promotion_rule_store.rb
+++ b/core/app/models/spree/promotion_rule_store.rb
@@ -4,7 +4,7 @@ module Spree
   class PromotionRuleStore < Spree::Base
     self.table_name = "spree_promotion_rules_stores"
 
-    belongs_to :promotion_rule, class_name: "Spree::PromotionRule"
-    belongs_to :store, class_name: "Spree::Store"
+    belongs_to :promotion_rule, class_name: "Spree::PromotionRule", optional: true
+    belongs_to :store, class_name: "Spree::Store", optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_taxon.rb b/core/app/models/spree/promotion_rule_taxon.rb
index ccf6e434556..7df3f008870 100644
--- a/core/app/models/spree/promotion_rule_taxon.rb
+++ b/core/app/models/spree/promotion_rule_taxon.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class PromotionRuleTaxon < Spree::Base
-    belongs_to :promotion_rule
-    belongs_to :taxon
+    belongs_to :promotion_rule, optional: true
+    belongs_to :taxon, optional: true
   end
 end
diff --git a/core/app/models/spree/promotion_rule_user.rb b/core/app/models/spree/promotion_rule_user.rb
index 432afb826ab..8f269533ccb 100644
--- a/core/app/models/spree/promotion_rule_user.rb
+++ b/core/app/models/spree/promotion_rule_user.rb
@@ -4,7 +4,7 @@ module Spree
   class PromotionRuleUser < Spree::Base
     self.table_name = 'spree_promotion_rules_users'
 
-    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule'
-    belongs_to :user, class_name: Spree::UserClassHandle.new
+    belongs_to :promotion_rule, class_name: 'Spree::PromotionRule', optional: true
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
   end
 end
diff --git a/core/app/models/spree/refund.rb b/core/app/models/spree/refund.rb
index e26ecc1ad8d..b8caf0a8879 100644
--- a/core/app/models/spree/refund.rb
+++ b/core/app/models/spree/refund.rb
@@ -2,9 +2,9 @@
 
 module Spree
   class Refund < Spree::Base
-    belongs_to :payment, inverse_of: :refunds
-    belongs_to :reason, class_name: 'Spree::RefundReason', foreign_key: :refund_reason_id
-    belongs_to :reimbursement, inverse_of: :refunds
+    belongs_to :payment, inverse_of: :refunds, optional: true
+    belongs_to :reason, class_name: 'Spree::RefundReason', foreign_key: :refund_reason_id, optional: true
+    belongs_to :reimbursement, inverse_of: :refunds, optional: true
 
     has_many :log_entries, as: :source
 
diff --git a/core/app/models/spree/reimbursement.rb b/core/app/models/spree/reimbursement.rb
index e4309166174..c1739ccabc7 100644
--- a/core/app/models/spree/reimbursement.rb
+++ b/core/app/models/spree/reimbursement.rb
@@ -4,8 +4,8 @@ module Spree
   class Reimbursement < Spree::Base
     class IncompleteReimbursementError < StandardError; end
 
-    belongs_to :order, inverse_of: :reimbursements
-    belongs_to :customer_return, inverse_of: :reimbursements, touch: true
+    belongs_to :order, inverse_of: :reimbursements, optional: true
+    belongs_to :customer_return, inverse_of: :reimbursements, touch: true, optional: true
 
     has_many :refunds, inverse_of: :reimbursement
     has_many :credits, inverse_of: :reimbursement, class_name: 'Spree::Reimbursement::Credit'
diff --git a/core/app/models/spree/reimbursement/credit.rb b/core/app/models/spree/reimbursement/credit.rb
index dac5a16235d..2119656b81e 100644
--- a/core/app/models/spree/reimbursement/credit.rb
+++ b/core/app/models/spree/reimbursement/credit.rb
@@ -6,8 +6,8 @@ class Credit < Spree::Base
       class_attribute :default_creditable_class
       self.default_creditable_class = Spree::StoreCredit
 
-      belongs_to :reimbursement, inverse_of: :credits
-      belongs_to :creditable, polymorphic: true
+      belongs_to :reimbursement, inverse_of: :credits, optional: true
+      belongs_to :creditable, polymorphic: true, optional: true
 
       validates :creditable, presence: true
 
diff --git a/core/app/models/spree/return_authorization.rb b/core/app/models/spree/return_authorization.rb
index 8aba85b7ee2..35a6d80b817 100644
--- a/core/app/models/spree/return_authorization.rb
+++ b/core/app/models/spree/return_authorization.rb
@@ -4,14 +4,14 @@ module Spree
   # Models the return of Inventory Units to a Stock Location for an Order.
   #
   class ReturnAuthorization < Spree::Base
-    belongs_to :order, class_name: 'Spree::Order', inverse_of: :return_authorizations
+    belongs_to :order, class_name: 'Spree::Order', inverse_of: :return_authorizations, optional: true
 
     has_many :return_items, inverse_of: :return_authorization, dependent: :destroy
     has_many :inventory_units, through: :return_items, dependent: :nullify
     has_many :customer_returns, through: :return_items
 
-    belongs_to :stock_location
-    belongs_to :reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id
+    belongs_to :stock_location, optional: true
+    belongs_to :reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id, optional: true
 
     before_create :generate_number
 
diff --git a/core/app/models/spree/return_item.rb b/core/app/models/spree/return_item.rb
index c67bdc33bcc..c07a1f59ab3 100644
--- a/core/app/models/spree/return_item.rb
+++ b/core/app/models/spree/return_item.rb
@@ -29,15 +29,15 @@ class ReturnItem < Spree::Base
     class_attribute :refund_amount_calculator
     self.refund_amount_calculator = Calculator::Returns::DefaultRefundAmount
 
-    belongs_to :return_authorization, inverse_of: :return_items
-    belongs_to :inventory_unit, inverse_of: :return_items
-    belongs_to :exchange_variant, class_name: 'Spree::Variant'
-    belongs_to :exchange_inventory_unit, class_name: 'Spree::InventoryUnit', inverse_of: :original_return_item
-    belongs_to :customer_return, inverse_of: :return_items
-    belongs_to :reimbursement, inverse_of: :return_items
-    belongs_to :preferred_reimbursement_type, class_name: 'Spree::ReimbursementType'
-    belongs_to :override_reimbursement_type, class_name: 'Spree::ReimbursementType'
-    belongs_to :return_reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id
+    belongs_to :return_authorization, inverse_of: :return_items, optional: true
+    belongs_to :inventory_unit, inverse_of: :return_items, optional: true
+    belongs_to :exchange_variant, class_name: 'Spree::Variant', optional: true
+    belongs_to :exchange_inventory_unit, class_name: 'Spree::InventoryUnit', inverse_of: :original_return_item, optional: true
+    belongs_to :customer_return, inverse_of: :return_items, optional: true
+    belongs_to :reimbursement, inverse_of: :return_items, optional: true
+    belongs_to :preferred_reimbursement_type, class_name: 'Spree::ReimbursementType', optional: true
+    belongs_to :override_reimbursement_type, class_name: 'Spree::ReimbursementType', optional: true
+    belongs_to :return_reason, class_name: 'Spree::ReturnReason', foreign_key: :return_reason_id, optional: true
 
     validate :eligible_exchange_variant
     validate :belongs_to_same_customer_order
diff --git a/core/app/models/spree/role_user.rb b/core/app/models/spree/role_user.rb
index 449049bd30a..c4aa044531c 100644
--- a/core/app/models/spree/role_user.rb
+++ b/core/app/models/spree/role_user.rb
@@ -3,8 +3,8 @@
 module Spree
   class RoleUser < Spree::Base
     self.table_name = "spree_roles_users"
-    belongs_to :role, class_name: "Spree::Role"
-    belongs_to :user, class_name: Spree::UserClassHandle.new
+    belongs_to :role, class_name: "Spree::Role", optional: true
+    belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
 
     after_create :auto_generate_spree_api_key
 
diff --git a/core/app/models/spree/shipment.rb b/core/app/models/spree/shipment.rb
index 3c6535fe1a0..1ddbffe9f23 100644
--- a/core/app/models/spree/shipment.rb
+++ b/core/app/models/spree/shipment.rb
@@ -4,8 +4,8 @@ module Spree
   # An order's planned shipments including tracking and cost.
   #
   class Shipment < Spree::Base
-    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :shipments
-    belongs_to :stock_location, class_name: 'Spree::StockLocation'
+    belongs_to :order, class_name: 'Spree::Order', touch: true, inverse_of: :shipments, optional: true
+    belongs_to :stock_location, class_name: 'Spree::StockLocation', optional: true
 
     has_many :adjustments, as: :adjustable, inverse_of: :adjustable, dependent: :delete_all
     has_many :inventory_units, dependent: :destroy, inverse_of: :shipment
diff --git a/core/app/models/spree/shipping_method.rb b/core/app/models/spree/shipping_method.rb
index 053528ade7b..008fb355811 100644
--- a/core/app/models/spree/shipping_method.rb
+++ b/core/app/models/spree/shipping_method.rb
@@ -28,7 +28,7 @@ class ShippingMethod < Spree::Base
     has_many :shipping_method_zones, dependent: :destroy
     has_many :zones, through: :shipping_method_zones
 
-    belongs_to :tax_category, -> { with_deleted }, class_name: 'Spree::TaxCategory'
+    belongs_to :tax_category, -> { with_deleted }, class_name: 'Spree::TaxCategory', optional: true
     has_many :shipping_method_stock_locations, dependent: :destroy, class_name: "Spree::ShippingMethodStockLocation"
     has_many :stock_locations, through: :shipping_method_stock_locations
 
diff --git a/core/app/models/spree/shipping_method_category.rb b/core/app/models/spree/shipping_method_category.rb
index 0d67a34506f..0a4072243a7 100644
--- a/core/app/models/spree/shipping_method_category.rb
+++ b/core/app/models/spree/shipping_method_category.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ShippingMethodCategory < Spree::Base
-    belongs_to :shipping_method, class_name: 'Spree::ShippingMethod'
-    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :shipping_method_categories
+    belongs_to :shipping_method, class_name: 'Spree::ShippingMethod', optional: true
+    belongs_to :shipping_category, class_name: 'Spree::ShippingCategory', inverse_of: :shipping_method_categories, optional: true
   end
 end
diff --git a/core/app/models/spree/shipping_method_stock_location.rb b/core/app/models/spree/shipping_method_stock_location.rb
index cadd852891d..792a584d8d5 100644
--- a/core/app/models/spree/shipping_method_stock_location.rb
+++ b/core/app/models/spree/shipping_method_stock_location.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
 class Spree::ShippingMethodStockLocation < Spree::Base
-  belongs_to :shipping_method
-  belongs_to :stock_location
+  belongs_to :shipping_method, optional: true
+  belongs_to :stock_location, optional: true
 end
diff --git a/core/app/models/spree/shipping_method_zone.rb b/core/app/models/spree/shipping_method_zone.rb
index 8262a60d3d9..c7526d0a298 100644
--- a/core/app/models/spree/shipping_method_zone.rb
+++ b/core/app/models/spree/shipping_method_zone.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class ShippingMethodZone < Spree::Base
-    belongs_to :zone
-    belongs_to :shipping_method
+    belongs_to :zone, optional: true
+    belongs_to :shipping_method, optional: true
   end
 end
diff --git a/core/app/models/spree/shipping_rate.rb b/core/app/models/spree/shipping_rate.rb
index c3d28f3afd7..2e7fe8c44d0 100644
--- a/core/app/models/spree/shipping_rate.rb
+++ b/core/app/models/spree/shipping_rate.rb
@@ -5,8 +5,8 @@ module Spree
   # method has been selected to deliver the shipment.
   #
   class ShippingRate < Spree::Base
-    belongs_to :shipment, class_name: 'Spree::Shipment', touch: true
-    belongs_to :shipping_method, -> { with_deleted }, class_name: 'Spree::ShippingMethod', inverse_of: :shipping_rates
+    belongs_to :shipment, class_name: 'Spree::Shipment', touch: true, optional: true
+    belongs_to :shipping_method, -> { with_deleted }, class_name: 'Spree::ShippingMethod', inverse_of: :shipping_rates, optional: true
 
     has_many :taxes,
              class_name: "Spree::ShippingRateTax",
diff --git a/core/app/models/spree/shipping_rate_tax.rb b/core/app/models/spree/shipping_rate_tax.rb
index 43b9d0dad09..c3528e4080c 100644
--- a/core/app/models/spree/shipping_rate_tax.rb
+++ b/core/app/models/spree/shipping_rate_tax.rb
@@ -7,8 +7,8 @@ module Spree
   # @since 1.3.0
   # @see Spree::Tax::ShippingRateTaxer
   class ShippingRateTax < ActiveRecord::Base
-    belongs_to :shipping_rate, class_name: "Spree::ShippingRate"
-    belongs_to :tax_rate, class_name: "Spree::TaxRate"
+    belongs_to :shipping_rate, class_name: "Spree::ShippingRate", optional: true
+    belongs_to :tax_rate, class_name: "Spree::TaxRate", optional: true
 
     extend DisplayMoney
     money_methods :absolute_amount
diff --git a/core/app/models/spree/state.rb b/core/app/models/spree/state.rb
index 7036cb63a71..503b0ea2d6a 100644
--- a/core/app/models/spree/state.rb
+++ b/core/app/models/spree/state.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class State < Spree::Base
-    belongs_to :country, class_name: 'Spree::Country'
+    belongs_to :country, class_name: 'Spree::Country', optional: true
     has_many :addresses, dependent: :nullify
 
     validates :country, :name, presence: true
diff --git a/core/app/models/spree/state_change.rb b/core/app/models/spree/state_change.rb
index d302287cba1..2e642c6d900 100644
--- a/core/app/models/spree/state_change.rb
+++ b/core/app/models/spree/state_change.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class StateChange < Spree::Base
-    belongs_to :user
-    belongs_to :stateful, polymorphic: true
+    belongs_to :user, optional: true
+    belongs_to :stateful, polymorphic: true, optional: true
     before_create :assign_user
 
     def <=>(other)
diff --git a/core/app/models/spree/stock_item.rb b/core/app/models/spree/stock_item.rb
index 0b4d2b6d27e..3836b1097fe 100644
--- a/core/app/models/spree/stock_item.rb
+++ b/core/app/models/spree/stock_item.rb
@@ -10,8 +10,8 @@ class StockItem < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :stock_items
-    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', inverse_of: :stock_items
+    belongs_to :stock_location, class_name: 'Spree::StockLocation', inverse_of: :stock_items, optional: true
+    belongs_to :variant, -> { with_deleted }, class_name: 'Spree::Variant', inverse_of: :stock_items, optional: true
     has_many :stock_movements, inverse_of: :stock_item
 
     validates :stock_location, :variant, presence: true
diff --git a/core/app/models/spree/stock_location.rb b/core/app/models/spree/stock_location.rb
index faa53f5d80f..eca5ab1d85c 100644
--- a/core/app/models/spree/stock_location.rb
+++ b/core/app/models/spree/stock_location.rb
@@ -16,8 +16,8 @@ class InvalidMovementError < StandardError; end
     has_many :user_stock_locations, dependent: :delete_all
     has_many :users, through: :user_stock_locations
 
-    belongs_to :state, class_name: 'Spree::State'
-    belongs_to :country, class_name: 'Spree::Country'
+    belongs_to :state, class_name: 'Spree::State', optional: true
+    belongs_to :country, class_name: 'Spree::Country', optional: true
 
     has_many :shipping_method_stock_locations, dependent: :destroy
     has_many :shipping_methods, through: :shipping_method_stock_locations
diff --git a/core/app/models/spree/stock_movement.rb b/core/app/models/spree/stock_movement.rb
index 4ab1c45cc98..c4c11cf929a 100644
--- a/core/app/models/spree/stock_movement.rb
+++ b/core/app/models/spree/stock_movement.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class StockMovement < Spree::Base
-    belongs_to :stock_item, class_name: 'Spree::StockItem', inverse_of: :stock_movements
-    belongs_to :originator, polymorphic: true
+    belongs_to :stock_item, class_name: 'Spree::StockItem', inverse_of: :stock_movements, optional: true
+    belongs_to :originator, polymorphic: true, optional: true
 
     after_create :update_stock_item_quantity
 
diff --git a/core/app/models/spree/store_credit.rb b/core/app/models/spree/store_credit.rb
index 970dacdd44b..9d33ec38b02 100644
--- a/core/app/models/spree/store_credit.rb
+++ b/core/app/models/spree/store_credit.rb
@@ -18,10 +18,10 @@ class Spree::StoreCredit < Spree::PaymentSource
   ADJUSTMENT_ACTION = 'adjustment'
   INVALIDATE_ACTION = 'invalidate'
 
-  belongs_to :user, class_name: Spree::UserClassHandle.new
-  belongs_to :created_by, class_name: Spree::UserClassHandle.new
-  belongs_to :category, class_name: "Spree::StoreCreditCategory"
-  belongs_to :credit_type, class_name: 'Spree::StoreCreditType', foreign_key: 'type_id'
+  belongs_to :user, class_name: Spree::UserClassHandle.new, optional: true
+  belongs_to :created_by, class_name: Spree::UserClassHandle.new, optional: true
+  belongs_to :category, class_name: "Spree::StoreCreditCategory", optional: true
+  belongs_to :credit_type, class_name: 'Spree::StoreCreditType', foreign_key: 'type_id', optional: true
   has_many :store_credit_events
 
   validates_presence_of :user_id, :category_id, :type_id, :created_by_id, :currency
diff --git a/core/app/models/spree/store_credit_event.rb b/core/app/models/spree/store_credit_event.rb
index 07c0294337d..02dda397a06 100644
--- a/core/app/models/spree/store_credit_event.rb
+++ b/core/app/models/spree/store_credit_event.rb
@@ -10,9 +10,9 @@ class StoreCreditEvent < Spree::Base
     include Discard::Model
     self.discard_column = :deleted_at
 
-    belongs_to :store_credit
-    belongs_to :originator, polymorphic: true
-    belongs_to :store_credit_reason, class_name: 'Spree::StoreCreditReason', inverse_of: :store_credit_events
+    belongs_to :store_credit, optional: true
+    belongs_to :originator, polymorphic: true, optional: true
+    belongs_to :store_credit_reason, class_name: 'Spree::StoreCreditReason', inverse_of: :store_credit_events, optional: true
 
     validates_presence_of :store_credit_reason, if: :action_requires_reason?
 
diff --git a/core/app/models/spree/store_payment_method.rb b/core/app/models/spree/store_payment_method.rb
index 64efc2ad34e..f1b0b0b177c 100644
--- a/core/app/models/spree/store_payment_method.rb
+++ b/core/app/models/spree/store_payment_method.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class StorePaymentMethod < Spree::Base
-    belongs_to :store, inverse_of: :store_payment_methods
-    belongs_to :payment_method, inverse_of: :store_payment_methods
+    belongs_to :store, inverse_of: :store_payment_methods, optional: true
+    belongs_to :payment_method, inverse_of: :store_payment_methods, optional: true
   end
 end
diff --git a/core/app/models/spree/store_shipping_method.rb b/core/app/models/spree/store_shipping_method.rb
index b8578c3aa0d..b98e9dacf55 100644
--- a/core/app/models/spree/store_shipping_method.rb
+++ b/core/app/models/spree/store_shipping_method.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class StoreShippingMethod < Spree::Base
-    belongs_to :store, inverse_of: :store_shipping_methods
-    belongs_to :shipping_method, inverse_of: :store_shipping_methods
+    belongs_to :store, inverse_of: :store_shipping_methods, optional: true
+    belongs_to :shipping_method, inverse_of: :store_shipping_methods, optional: true
   end
 end
diff --git a/core/app/models/spree/tax_rate.rb b/core/app/models/spree/tax_rate.rb
index 427aeaaf6ff..b113ac6c1b4 100644
--- a/core/app/models/spree/tax_rate.rb
+++ b/core/app/models/spree/tax_rate.rb
@@ -17,7 +17,7 @@ class TaxRate < Spree::Base
     include Spree::CalculatedAdjustments
     include Spree::AdjustmentSource
 
-    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates
+    belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates, optional: true
 
     has_many :tax_rate_tax_categories,
       class_name: 'Spree::TaxRateTaxCategory',
diff --git a/core/app/models/spree/tax_rate_tax_category.rb b/core/app/models/spree/tax_rate_tax_category.rb
index 6f8270391d2..e68f89c7ac7 100644
--- a/core/app/models/spree/tax_rate_tax_category.rb
+++ b/core/app/models/spree/tax_rate_tax_category.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class TaxRateTaxCategory < Spree::Base
-    belongs_to :tax_rate, class_name: 'Spree::TaxRate', inverse_of: :tax_rate_tax_categories
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory', inverse_of: :tax_rate_tax_categories
+    belongs_to :tax_rate, class_name: 'Spree::TaxRate', inverse_of: :tax_rate_tax_categories, optional: true
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', inverse_of: :tax_rate_tax_categories, optional: true
   end
 end
diff --git a/core/app/models/spree/unit_cancel.rb b/core/app/models/spree/unit_cancel.rb
index d54c78ac614..1b4bbf947fc 100644
--- a/core/app/models/spree/unit_cancel.rb
+++ b/core/app/models/spree/unit_cancel.rb
@@ -7,7 +7,7 @@ class Spree::UnitCancel < Spree::Base
   SHORT_SHIP = 'Short Ship'
   DEFAULT_REASON = 'Cancel'
 
-  belongs_to :inventory_unit
+  belongs_to :inventory_unit, optional: true
   has_one :adjustment, as: :source, dependent: :destroy
 
   validates :inventory_unit, presence: true
diff --git a/core/app/models/spree/user_address.rb b/core/app/models/spree/user_address.rb
index b060aea55c6..3e60b46fd82 100644
--- a/core/app/models/spree/user_address.rb
+++ b/core/app/models/spree/user_address.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class UserAddress < Spree::Base
-    belongs_to :user, class_name: UserClassHandle.new, foreign_key: "user_id"
-    belongs_to :address, class_name: "Spree::Address"
+    belongs_to :user, class_name: UserClassHandle.new, foreign_key: "user_id", optional: true
+    belongs_to :address, class_name: "Spree::Address", optional: true
 
     validates_uniqueness_of :address_id, scope: :user_id
     validates_uniqueness_of :user_id, conditions: -> { active.default }, message: :default_address_exists, if: :default?
diff --git a/core/app/models/spree/user_stock_location.rb b/core/app/models/spree/user_stock_location.rb
index b627a0df9b1..c3c92d595b5 100644
--- a/core/app/models/spree/user_stock_location.rb
+++ b/core/app/models/spree/user_stock_location.rb
@@ -2,7 +2,7 @@
 
 module Spree
   class UserStockLocation < Spree::Base
-    belongs_to :user, class_name: Spree::UserClassHandle.new, inverse_of: :user_stock_locations
-    belongs_to :stock_location, class_name: "Spree::StockLocation", inverse_of: :user_stock_locations
+    belongs_to :user, class_name: Spree::UserClassHandle.new, inverse_of: :user_stock_locations, optional: true
+    belongs_to :stock_location, class_name: "Spree::StockLocation", inverse_of: :user_stock_locations, optional: true
   end
 end
diff --git a/core/app/models/spree/variant.rb b/core/app/models/spree/variant.rb
index e41f269795c..b0b18b0d393 100644
--- a/core/app/models/spree/variant.rb
+++ b/core/app/models/spree/variant.rb
@@ -37,7 +37,7 @@ class Variant < Spree::Base
     include Spree::DefaultPrice
 
     belongs_to :product, -> { with_deleted }, touch: true, class_name: 'Spree::Product', inverse_of: :variants, optional: false
-    belongs_to :tax_category, class_name: 'Spree::TaxCategory'
+    belongs_to :tax_category, class_name: 'Spree::TaxCategory', optional: true
 
     delegate :name, :description, :slug, :available_on, :shipping_category_id,
              :meta_description, :meta_keywords, :shipping_category,
diff --git a/core/app/models/spree/variant_property_rule.rb b/core/app/models/spree/variant_property_rule.rb
index e41f06a97da..ff6bb376a88 100644
--- a/core/app/models/spree/variant_property_rule.rb
+++ b/core/app/models/spree/variant_property_rule.rb
@@ -13,7 +13,7 @@
 # targeted by the rule, the properties will automatically apply to the variant.
 module Spree
   class VariantPropertyRule < Spree::Base
-    belongs_to :product, touch: true
+    belongs_to :product, touch: true, optional: true
 
     has_many :values, class_name: 'Spree::VariantPropertyRuleValue', dependent: :destroy
     has_many :properties, through: :values
diff --git a/core/app/models/spree/variant_property_rule_condition.rb b/core/app/models/spree/variant_property_rule_condition.rb
index de03c78dfe4..7670d842a0a 100644
--- a/core/app/models/spree/variant_property_rule_condition.rb
+++ b/core/app/models/spree/variant_property_rule_condition.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class VariantPropertyRuleCondition < Spree::Base
-    belongs_to :option_value
-    belongs_to :variant_property_rule, touch: true
+    belongs_to :option_value, optional: true
+    belongs_to :variant_property_rule, touch: true, optional: true
 
     validates_uniqueness_of :option_value_id, scope: :variant_property_rule_id
   end
diff --git a/core/app/models/spree/variant_property_rule_value.rb b/core/app/models/spree/variant_property_rule_value.rb
index 44c3de9595d..d030841cd55 100644
--- a/core/app/models/spree/variant_property_rule_value.rb
+++ b/core/app/models/spree/variant_property_rule_value.rb
@@ -6,7 +6,7 @@ class VariantPropertyRuleValue < Spree::Base
 
     acts_as_list scope: :variant_property_rule
 
-    belongs_to :property
-    belongs_to :variant_property_rule, touch: true
+    belongs_to :property, optional: true
+    belongs_to :variant_property_rule, touch: true, optional: true
   end
 end
diff --git a/core/app/models/spree/wallet_payment_source.rb b/core/app/models/spree/wallet_payment_source.rb
index d79e0e2d907..16f5f298c3d 100644
--- a/core/app/models/spree/wallet_payment_source.rb
+++ b/core/app/models/spree/wallet_payment_source.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class WalletPaymentSource < Spree::Base
-    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', inverse_of: :wallet_payment_sources
-    belongs_to :payment_source, polymorphic: true, inverse_of: :wallet_payment_sources
+    belongs_to :user, class_name: Spree::UserClassHandle.new, foreign_key: 'user_id', inverse_of: :wallet_payment_sources, optional: true
+    belongs_to :payment_source, polymorphic: true, inverse_of: :wallet_payment_sources, optional: true
 
     validates_presence_of :user
     validates_presence_of :payment_source
diff --git a/core/app/models/spree/zone_member.rb b/core/app/models/spree/zone_member.rb
index 17e9f9aece4..a2ac6f63d68 100644
--- a/core/app/models/spree/zone_member.rb
+++ b/core/app/models/spree/zone_member.rb
@@ -2,8 +2,8 @@
 
 module Spree
   class ZoneMember < Spree::Base
-    belongs_to :zone, class_name: 'Spree::Zone', counter_cache: true, inverse_of: :zone_members
-    belongs_to :zoneable, polymorphic: true
+    belongs_to :zone, class_name: 'Spree::Zone', counter_cache: true, inverse_of: :zone_members, optional: true
+    belongs_to :zoneable, polymorphic: true, optional: true
 
     delegate :name, to: :zoneable, allow_nil: true
   end