`no method matching children(::Cthulhu.Callsite)` on step into Union Call.

 • %75 = call → copyto_nonleaf!(::Union{Vector{Int8}, Vector{Nothing}}{…},::Broadcasted{…},::OneTo{…},::Int64,::Int64)::…
   ↩
ERROR: MethodError: no method matching children(::Cthulhu.Callsite)

Closest candidates are:
  children(::JuliaSyntax.GreenNode)
   @ JuliaSyntax ~/.julia/packages/JuliaSyntax/DHdTk/src/green_tree.jl:67
  children(::JuliaSyntax.TreeNode)
   @ JuliaSyntax ~/.julia/packages/JuliaSyntax/DHdTk/src/syntax_tree.jl:152

Stacktrace:
  [1] (::Cthulhu.var"#91#98"{Cthulhu.Callsite, Cthulhu.Callsite})(ci::Cthulhu.ConstPropCallInfo)
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:581
  [2] iterate(::Base.Generator{Vector{Cthulhu.CallInfo}, Cthulhu.var"#91#98"{Cthulhu.Callsite, Cthulhu.Callsite}})
    @ Base ./generator.jl:47 [inlined]
  [3] _collect(c::Vector{Cthulhu.CallInfo}, itr::Base.Generator{Vector{Cthulhu.CallInfo}, Cthulhu.var"#91#98"{Cthulhu.Callsite, Cthulhu.Callsite}}, ::Base.EltypeUnknown, isz::Base.HasShape{1})
    @ Base ./array.jl:847 [inlined]
  [4] collect_similar(cont::Vector{Cthulhu.CallInfo}, itr::Base.Generator{Vector{Cthulhu.CallInfo}, Cthulhu.var"#91#98"{Cthulhu.Callsite, Cthulhu.Callsite}})
    @ Base ./array.jl:756
  [5] map(f::Function, A::Vector{Cthulhu.CallInfo})
    @ Base ./abstractarray.jl:3267
  [6] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, curs::Cthulhu.CthulhuCursor; override::Nothing, debuginfo::Cthulhu.DInfo.DebugInfo, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, with_effects::Bool, inline_cost::Bool, type_annotations::Bool, annotate_source::Bool)
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:579
  [7] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, curs::Cthulhu.CthulhuCursor; override::Nothing, debuginfo::Cthulhu.DInfo.DebugInfo, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, with_effects::Bool, inline_cost::Bool, type_annotations::Bool, annotate_source::Bool)
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:634
  [8] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, curs::Cthulhu.CthulhuCursor; override::Nothing, debuginfo::Symbol, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, with_effects::Bool, inline_cost::Bool, type_annotations::Bool, annotate_source::Bool)
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:634
  [9] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, mi::Core.MethodInstance; kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, @NamedTuple{iswarn::Bool}})
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:770
 [10] _descend(term::REPL.Terminals.TTYTerminal, args::Any; interp::Core.Compiler.NativeInterpreter, kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, @NamedTuple{iswarn::Bool}})
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:786
 [11] __descend_with_error_handling(args::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/packages/Cthulhu/KIvdU/src/Cthulhu.jl:244
 [12] _descend_with_error_handling(f::Any, argtypes::Any; kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, @NamedTuple{iswarn::Bool}})
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:233
 [13] descend_code_typed(::Any, ::Vararg{Any}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}})
    @ Cthulhu ~/.julia/packages/Cthulhu/KIvdU/src/Cthulhu.jl:178
 [14] top-level scope
    @ REPL[2]:1

Reproduce the failure by stepping into the shown Union call with descend_code_typed, then inspect Cthulhu.jl around lines 579, 634, 770 and the Callsite handling in the stack trace. Trace why children is called on Cthulhu.Callsite; done means stepping into this call no longer raises the reported MethodError.