Hidden backwards compatibility issue?

[grahamas]

I get the following error with the attached file. Here's a file that's causing the problem (renamed to txt, hoping Github won't get mad).
ensemble_solution.txt

I eventually figured out that the problem was that I was trying to load using JuliaDB v0.9 and the file was saved with v0.13. I realize that backwards compatibility isn't guaranteed, but it would be nice to have a more informative error message.

(side note: a higher priority for me would be getting the Nullables dependency upgraded/removed, as that creates a dependency on a very old Compat, which is why I accidentally got stuck on JuliaDB v0.9)

ERROR: LoadError: UndefVarError: T not defined
Stacktrace:
 [1] deserialize(::Serialization.Serializer{IOStream}, ::Type{MemPool.MMSer{IndexedTables.NDSparse{T,D<:Tuple,C<:IndexedTables.Columns,V} where V<:(AbstractArray{T,1} where T)}}) at /home/graham/.julia/packages/MemPool/tlPqB/src/io.jl:27
 [2] handle_deserialize(::Serialization.Serializer{IOStream}, ::Int32) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:837
 [3] deserialize(::Serialization.Serializer{IOStream}) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:773
 [4] handle_deserialize(::Serialization.Serializer{IOStream}, ::Int32) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:879
 [5] deserialize(::Serialization.Serializer{IOStream}) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:773
 [6] deserialize at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Serialization/src/Serialization.jl:760 [inlined]
 [7] open(::typeof(Serialization.deserialize), ::String; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at ./io.jl:325
 [8] open at ./io.jl:323 [inlined]
 [9] load(::String) at /home/graham/.julia/packages/JuliaDB/vRAcT/src/io.jl:184