fix undef sparam in locals (#201)

Author: KristofferC

src/utils.jl

@@ -303,7 +303,9 @@ function locals(frame::Frame)
     if code.scope isa Method
         syms = sparam_syms(code.scope)
         for i in 1:length(syms)
-            push!(vars, Variable(data.sparams[i], syms[i], true))
+            if isassigned(data.sparams, i)
+                push!(vars, Variable(data.sparams[i], syms[i], true))
+            end
         end
     end
     return vars

test/interpret.jl

@@ -413,3 +413,8 @@ e = try
     end
 @test e isa UndefVarError
 @test e.var == :S
+# https://github.com/JuliaDebug/JuliaInterpreter.jl/issues/200
+locs = JuliaInterpreter.locals(JuliaInterpreter.enter_call(foo, ""))
+@test length(locs) == 3 # #self# + 2 variables
+@test JuliaInterpreter.Variable("", :x, false) in locs
+@test JuliaInterpreter.Variable(String, :T, true) in locs