fix: empty dictionary when receiving null

Author: AndyEveritt

src/dsf/object_model/utils.py

@@ -33,7 +33,9 @@ def is_model_object(o: object) -> bool:
 
 
 def _set_model_prop(instance: object, name: str, runtime_type: type[JSONElement | datetime], current_value: T, value: Union[T, JSONElement]):
-    if isinstance(value, dict):  # Update from JSON
+    if value is None and isinstance(current_value, ModelDictionary):  # DSF sends null to clear a dictionary
+        current_value.update_from_json(cast(JSONObj, None))
+    elif isinstance(value, dict):  # Update from JSON
         if not isinstance(current_value, (ModelObject, ModelDictionary)):
             raise TypeError(f"{instance.__class__.__name__}.{name} must be of type ModelObject or ModelDictionary to update from a dict."
                             f" Got {type(current_value).__name__}: {current_value}")

tests/test_object_model.py

@@ -424,6 +424,16 @@ def test_rc2_fields(self):
         model.update_from_json('{"move": {"shaping": {"type": "eI3"}}}')
         self.assertEqual(model.move.shaping.type, InputShapingType.ei3)
 
+    def test_null_clears_dictionary(self):
+        # DSF sends null for a dictionary that has been cleared, e.g. job.file.customInfo when a job ends
+        model = ObjectModel()
+        model.update_from_json({"job": {"file": {"customInfo": {"material": "PETG"}}}})
+        self.assertEqual(dict(model.job.file.custom_info), {"material": "PETG"})
+        custom_info = model.job.file.custom_info
+        model.update_from_json({"job": {"file": {"customInfo": None}}})
+        self.assertIs(model.job.file.custom_info, custom_info)
+        self.assertEqual(dict(model.job.file.custom_info), {})
+
     def test_global(self):
         # "global" is a Python keyword so the JSON key is exposed as ObjectModel.globals
         with open('tests/object_model/model_full.json') as fp: