fix debugger crash when stackframe does not have args

Author: lukaszsamson

apps/elixir_ls_debugger/lib/debugger/server.ex

@@ -1108,13 +1108,15 @@ defmodule ElixirLS.Debugger.Server do
             "expensive" => false
           }
 
-          args_scope = %{
-            "name" => "arguments",
-            "variablesReference" => args_id,
-            "namedVariables" => 0,
-            "indexedVariables" => Enum.count(frame.args),
-            "expensive" => false
-          }
+          args_scope = if frame.args != :undefined do
+            %{
+              "name" => "arguments",
+              "variablesReference" => args_id,
+              "namedVariables" => 0,
+              "indexedVariables" => Enum.count(frame.args),
+              "expensive" => false
+            }
+          end
 
           messages_scope = %{
             "name" => "messages",
@@ -1134,7 +1136,7 @@ defmodule ElixirLS.Debugger.Server do
 
           scopes =
             [vars_scope, versioned_vars_scope, process_info_scope]
-            |> Kernel.++(if Enum.count(frame.args) > 0, do: [args_scope], else: [])
+            |> Kernel.++(if frame.args != :undefined and Enum.count(frame.args) > 0, do: [args_scope], else: [])
             |> Kernel.++(if Enum.count(frame.messages) > 0, do: [messages_scope], else: [])
 
           {state, scopes}