MethodInstance not found

To reproduce checkout https://github.com/simeonschaub/SchurPolynomials.jl/tree/sds/invoke and run the following:

julia> using SchurPolynomials, Transducers, Cthulhu

julia> using AbstractAlgebra: Partition

julia> SSYT = SchurPolynomials.SemiStandardYoungTableaux(6, Partition([3, 2, 1]));

julia> @descend SchurPolynomials._worker!(1, Transducers.BottomRF(Transducers.SideEffect(identity)), nothing, SSYT)
_worker!(i, rf::RF, acc, ssyt) where RF in SchurPolynomials at /home/simeon/Documents/MIT/18.338/Project/SchurPolynomials/src/SchurPolynomials.jl:56
[...]

Press enter a bunch of times until the IR for the function _row! is shown and then select the second of the two invoke statements to _row! again below:

[...]
   %22  = invoke next(::BottomRF{…},::Nothing,::Nothing)::AbstractAlgebra.Generic.YoungTableau{Int64}
   %57  = invoke throw_boundserror(::SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true},::Tuple{Int64})::Union{}
   %121  = invoke throw_boundserror(::SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true},::Tuple{Int64})::Union{}
   %168  = invoke _row!(::Int64,::Int64,::SubArray{…},::Array{…},::Int64,::BottomRF{…},::Nothing)::Any
 • %173  = invoke _row!(::Int64,::Int64,::SubArray{…},::Array{…},::Int64,::BottomRF{…},::YoungTableau{…})::Any
   ↩
ERROR: KeyError: key MethodInstance for SchurPolynomials._row!(::Int64, ::Int64, ::SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, ::Vector{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}}, ::Int64, ::Transducers.BottomRF{Completing{SchurPolynomials.var"#3#4"{Int64, Transducers.BottomRF{Transducers.SideEffect{typeof(identity)}}, SchurPolynomials.SemiStandardYoungTableaux}}}, ::AbstractAlgebra.Generic.YoungTableau{Int64}) not found
Stacktrace:
 [1] getindex(h::Dict{Core.MethodInstance, Core.CodeInstance}, key::Core.MethodInstance)
   @ Base ./dict.jl:498
 [2] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, mi::Core.MethodInstance; override::Nothing, debuginfo::Cthulhu.DInfo.DebugInfo, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, inline_cost::Bool, type_annotations::Bool)
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:249
 [3] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, mi::Core.MethodInstance; override::Nothing, debuginfo::Cthulhu.DInfo.DebugInfo, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, inline_cost::Bool, type_annotations::Bool) (repeats 15 times)
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:379
 [4] _descend(::REPL.Terminals.TTYTerminal, ::Any, ::Vararg{Any}; interp::Core.Compiler.NativeInterpreter, kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, NamedTuple{(:iswarn,), Tuple{Bool}}})
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:496
 [5] _descend_with_error_handling(::Any, ::Vararg{Any}; terminal::Any, kwargs::Base.Pairs{Symbol, V, Tuple{Vararg{Symbol, N}}, NamedTuple{names, T}} where {V, N, names, T<:Tuple{Vararg{Any, N}}})
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:148
 [6] descend_code_typed(f::Function, tt::Any; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:120
 [7] descend_code_typed(f::Function, tt::Any)
   @ Cthulhu ~/.julia/dev/Cthulhu/src/Cthulhu.jl:120
 [8] top-level scope
   @ REPL[4]:1

So it seems that Cthulhu is somehow not handling the union split input types together with the widened return type due to bounded recursion correctly.