lambda map - null values turning into empty string?

[coolhome]

Bicep version
az bicep version
Bicep CLI version 0.11.1 (030248d)

Describe the bug
Mapping subnets from existing virtualNetwork and unable to make properties null?

To Reproduce
Steps to reproduce the behavior:

targetScope = 'resourceGroup'

param virtualNetworkName string

resource vnet 'Microsoft.Network/virtualNetworks@2022-05-01' existing = {
  name: virtualNetworkName
}

output subnets array = map(vnet.properties.subnets, subnet => {
  name: subnet.name
  addressPrefix: subnet.properties.addressPrefix
  applicationGatewayIpConfigurations: contains(subnet.properties, 'applicationGatewayIpConfigurations') ? subnet.properties.applicationGatewayIpConfigurations : []
  delegations: contains(subnet.properties, 'delegations') ? subnet.properties.delegations : []
  ipAllocations: contains(subnet.properties, 'ipAllocations') ? subnet.properties.ipAllocations : []
  natGatewayId: contains(subnet.properties, 'natGateway') ? subnet.properties.natGateway.id : null
  networkSecurityGroupId: contains(subnet.properties, 'networkSecurityGroup') ? subnet.properties.networkSecurityGroup.id : null
  privateEndpointNetworkPolicies: contains(subnet.properties, 'privateEndpointNetworkPolicies') ? subnet.properties.privateEndpointNetworkPolicies : null
  privateLinkServiceNetworkPolicies: contains(subnet.properties, 'privateLinkServiceNetworkPolicies') ? subnet.properties.privateLinkServiceNetworkPolicies : null
  routeTableId: contains(subnet.properties, 'routeTable') && contains(subnet.properties.routeTable, 'id') && !empty(subnet.properties.routeTable.id) ? subnet.properties.routeTable.id : null
  serviceEndpoints: contains(subnet.properties, 'serviceEndpoints') ? subnet.properties.serviceEndpoints : []
  serviceEndpointPolicies: contains(subnet.properties, 'serviceEndpointPolicies') ? subnet.properties.serviceEndpointPolicies : []
})

output subnetsRaw array = vnet.properties.subnets

Why is routeTableId an empty string if it does not exist in subnetsRaw? I imagine the following line would of worked to remove non existing resources?

  routeTableId: contains(subnet.properties, 'routeTable') && contains(subnet.properties.routeTable, 'id') && !empty(subnet.properties.routeTable.id) ? subnet.properties.routeTable.id : null

Example here shows this should work - https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/bicep-functions-object#example-1

[alex-frankel]

Closing and tracking with #8782