nested_set raises KeyError if not create_missing

libbot/sync/__init__.py

@@ -55,7 +55,9 @@ def nested_set(target: dict, value: Any, *path: str, create_missing=True) -> dic
         elif create_missing:
             d = d.setdefault(key, {})
         else:
-            return target
+            raise KeyError(
+                f"Key '{key}' is not found under path provided ({path}) and create_missing is False"
+            )
     if path[-1] in d or create_missing:
         d[path[-1]] = value
     return target