ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}

[fredrikekre]

I don't have a MWE for this (yet), but I get the following error in the Debugger.

ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
  [1] specialize_method(method::Method, atype::Any, sparams::Core.SimpleVector; preexisting::Bool, compilesig::Bool)
    @ Core.Compiler ./compiler/utilities.jl:207
  [2] specialize_method
    @ ./compiler/utilities.jl:193 [inlined]
  [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:754
  [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:774
  [5] showerror(io::IOContext{IOBuffer}, ex::TypeError, bt::JuliaInterpreter.Frame; backtrace::Bool)
    @ Base ./errorshow.jl:90
  [6] showerror
    @ ./errorshow.jl:86 [inlined]
  [7] display_error(io::IOContext{IOBuffer}, er::TypeError, frame::JuliaInterpreter.Frame)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:794
  [8] (::Debugger.var"#10#19"{REPL.LineEdit.Prompt, Debugger.DebuggerState})(s::REPL.LineEdit.MIState, buf::IOBuffer, ok::Bool)
    @ Debugger ~/.julia/packages/Debugger/XLUtz/src/repl.jl:72

As a clue, the code I am debugging is broken, and in particular there is a MethodError thrown when running outside the Debugger.

[fredrikekre]

This might be a better stacktrace (from @run instead of stepping):

ERROR: TypeError: in specializations, expected DataType, got Type{Union{}}
Stacktrace:
 [1] specialize_method(method::Method, atype::Any, sparams::Core.SimpleVector; preexisting::Bool, compilesig::Bool)
   @ Core.Compiler ./compiler/utilities.jl:207
 [2] specialize_method
   @ ./compiler/utilities.jl:193 [inlined]
 [3] Base.StackTraces.StackFrame(frame::JuliaInterpreter.Frame)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:754
 [4] show_backtrace(io::IOContext{IOBuffer}, frame::JuliaInterpreter.Frame)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:774
 [5] showerror(io::IOContext{IOBuffer}, ex::MethodError, bt::JuliaInterpreter.Frame; backtrace::Bool)
   @ Base ./errorshow.jl:90
 [6] showerror
   @ ./errorshow.jl:86 [inlined]
 [7] display_error(io::IOContext{IOBuffer}, er::MethodError, frame::JuliaInterpreter.Frame)
   @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/utils.jl:794
 [8] RunDebugger(frame::JuliaInterpreter.Frame, repl::Nothing, terminal::Nothing; initial_continue::Bool)
   @ Debugger ~/.julia/packages/Debugger/XLUtz/src/repl.jl:157
 [9] top-level scope
   @ ~/.julia/packages/Debugger/XLUtz/src/Debugger.jl:137

caused by: MethodError: Cannot `convert` an object of type
  Tensor{2,2,Float64{},4} to an object of type
  Tensor{1,2,Float64{},2}
Stacktrace:
  [1] prepare_call(f::Any, allargs::Vector{Any}; enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/construct.jl:250
  [2] get_call_framecode(fargs::Vector{Any}, parentframe::JuliaInterpreter.FrameCode, idx::Int64; enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/localmethtable.jl:63
  [3] evaluate_call_recurse!(recurse::Any, frame::JuliaInterpreter.Frame, call_expr::Expr; enter_generated::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/interpret.jl:245
  [4] evaluate_call_recurse!
    @ ~/.julia/packages/JuliaInterpreter/ktCFr/src/interpret.jl:220 [inlined]
  [5] eval_rhs(recurse::Any, frame::JuliaInterpreter.Frame, node::Expr)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/interpret.jl:393
  [6] step_expr!(recurse::Any, frame::JuliaInterpreter.Frame, node::Any, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/interpret.jl:546
  [7] step_expr!(recurse::Any, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/interpret.jl:596
  [8] finish!(recurse::Any, frame::JuliaInterpreter.Frame, istoplevel::Bool)
    @ JuliaInterpreter ~/.julia/packages/JuliaInterpreter/ktCFr/src/commands.jl:14
  [9] finish_and_return!(recurse::Any, frame::JuliaInterpreter.Frame, istoplevel::Bool)