diff --git a/src/data/custom_serialization.jl b/src/data/custom_serialization.jl
index b49a5f92..fcb4de1d 100644
--- a/src/data/custom_serialization.jl
+++ b/src/data/custom_serialization.jl
@@ -2,7 +2,6 @@
 
 # The default, write a type as itself
 writeas(T::Type) = T
-writeas(::Type{Union{}}, slurp...) = (@assert isempty(slurp); Union{})
 
 # wconvert and rconvert do type conversion before reading and writing,
 # respectively. These fall back to convert.
@@ -66,4 +65,4 @@ function jlconvert(::ReadRepresentation{T,CustomSerialization{S,ODR}},
         track_weakref!(f, header_offset, v)
         return v
     end
-end
+end
\ No newline at end of file
diff --git a/src/data/specialcased_types.jl b/src/data/specialcased_types.jl
index 1a021272..5efcc4cc 100644
--- a/src/data/specialcased_types.jl
+++ b/src/data/specialcased_types.jl
@@ -246,7 +246,9 @@ rconvert(::Type{Core.SimpleVector}, x::Vector{Any}) = Core.svec(x...)
 
 ## Dicts
 
-writeas(::Type{<:AbstractDict{K,V}}) where {K,V} = Vector{Pair{K,V}}
+writeas(::Type{Dict{K,V}}) where {K,V} = Vector{Pair{K,V}}
+writeas(::Type{IdDict{Any,Any}}) = Vector{Pair{Any,Any}}
+writeas(::Type{Base.ImmutableDict{K,V}}) where {K,V} = Vector{Pair{K,V}}
 wconvert(::Type{Vector{Pair{K,V}}}, x::AbstractDict{K,V}) where {K,V} = collect(x)
 function rconvert(::Type{T}, x::Vector{Pair{K,V}}) where {T<:AbstractDict,K,V}
     d = T()
@@ -284,4 +286,4 @@ function writeas(NT::Type{NTuple{N,T}}) where {N,T}
 end
 
 wconvert(::Type{Vector{T}}, x::NTuple{N,T}) where {N,T} = collect(x)
-rconvert(::Type{NTuple{N,T}}, x::Vector{T}) where {N,T} = NTuple{N,T}(x)
+rconvert(::Type{NTuple{N,T}}, x::Vector{T}) where {N,T} = NTuple{N,T}(x)
\ No newline at end of file