fix #31760, regression in Dict iterate (#31762)

base/dict.jl

@@ -662,17 +662,17 @@ function skip_deleted(h::Dict, i)
  return i
  end
  end
- return nothing
+ return 0
 end
 function skip_deleted_floor!(h::Dict)
  idx = skip_deleted(h, h.idxfloor)
- if idx !== nothing
+ if idx != 0
  h.idxfloor = idx
  end
  idx
 end
 
-@propagate_inbounds _iterate(t::Dict{K,V}, i) where {K,V} = i === nothing ? nothing : (Pair{K,V}(t.keys[i],t.vals[i]), i == typemax(Int) ? nothing : i+1)
+@propagate_inbounds _iterate(t::Dict{K,V}, i) where {K,V} = i == 0 ? nothing : (Pair{K,V}(t.keys[i],t.vals[i]), i == typemax(Int) ? 0 : i+1)
 @propagate_inbounds function iterate(t::Dict)
  _iterate(t, skip_deleted_floor!(t))
 end
@@ -681,12 +681,12 @@ end
 isempty(t::Dict) = (t.count == 0)
 length(t::Dict) = t.count
 
-@propagate_inbounds function Base.iterate(v::T, i::Union{Int,Nothing}=v.dict.idxfloor) where T <: Union{KeySet{<:Any, <:Dict}, ValueIterator{<:Dict}}
- i === nothing && return nothing # This is to catch nothing returned when i = typemax
+@propagate_inbounds function Base.iterate(v::T, i::Int = v.dict.idxfloor) where T <: Union{KeySet{<:Any, <:Dict}, ValueIterator{<:Dict}}
+ i == 0 && return nothing
  i = skip_deleted(v.dict, i)
- i === nothing && return nothing # This is to catch nothing returned by skip_deleted
+ i == 0 && return nothing
  vals = T <: KeySet ? v.dict.keys : v.dict.vals
- (@inbounds vals[i], i == typemax(Int) ? nothing : i+1)
+ (@inbounds vals[i], i == typemax(Int) ? 0 : i+1)
 end
 
 filter!(f, d::Dict) = filter_in_one_pass!(f, d)