Exclude Union{} from is_vararg_type

Author: timholy

src/utils.jl

@@ -148,7 +148,7 @@ is_leaf(frame::Frame) = frame.callee === nothing
 
 function is_vararg_type(x)
     if isa(x, Type)
-        x <: Vararg && return true
+        (x <: Vararg && !(x <: Union{})) && return true
         if isa(x, UnionAll)
             x = Base.unwrap_unionall(x)
         end

test/interpret.jl

@@ -99,6 +99,7 @@ end
 # issue #6
 @test @interpret(Array.body.body.name) === Array.body.body.name
 @test @interpret(Vararg.body.body.name) === Vararg.body.body.name
+@test !JuliaInterpreter.is_vararg_type(Union{})
 frame = JuliaInterpreter.prepare_thunk(Main, :(Vararg.body.body.name))
 @test JuliaInterpreter.finish_and_return!(frame, true) === Vararg.body.body.name
 frame = JuliaInterpreter.prepare_thunk(Base, :(Union{AbstractChar,Tuple{Vararg{<:AbstractChar}},AbstractVector{<:AbstractChar},Set{<:AbstractChar}}))