do not stringify none return value (#148)

Author: saartochner-lumigo

src/lumigo_tracer/spans_container.py

@@ -260,7 +260,8 @@ def end(self, ret_val=None) -> Optional[int]:
         parsed_ret_val = None
         if Configuration.verbose:
             try:
-                parsed_ret_val = lumigo_dumps(ret_val, enforce_jsonify=True, decimal_safe=True)
+                if ret_val is not None:
+                    parsed_ret_val = lumigo_dumps(ret_val, enforce_jsonify=True, decimal_safe=True)
             except Exception as err:
                 suffix = ""
                 if err.args:

src/test/unit/test_spans_container.py

@@ -33,6 +33,13 @@ def test_spans_container_not_send_start_span_on_send_only_on_errors_mode(monkeyp
     assert _is_start_span_sent() is False
 
 
+def test_spans_container_end_function_got_none_return_value(monkeypatch):
+    SpansContainer.create_span()
+    SpansContainer.get_span().start()
+    SpansContainer.get_span().end(None)
+    assert SpansContainer.get_span().function_span["return_value"] is None
+
+
 def test_spans_container_end_function_not_send_spans_on_send_only_on_errors_mode(
     monkeypatch, dummy_http_request
 ):