add assertion for update_diff and not diff attribute.

Author: MarcelGeo

server/mergin/sync/files.py

@@ -286,8 +286,6 @@ def to_data_delta(self):
             change=self.change,
             version=self.version,
         )
-        if self.diffs:
-            result.diff = None
         return result
 
 
@@ -332,6 +330,9 @@ def make_object(self, data, **kwargs):
 
     @post_dump
     def patch_field(self, data, **kwargs):
+        assert data.get("change") != PushChangeType.UPDATE_DIFF.value or data.get(
+            "diff"
+        ), "Diff file must be provided for update_diff change type"
         # drop 'diff' key entirely if empty or None as database would expect
         if not data.get("diff"):
             data.pop("diff", None)

server/mergin/sync/models.py

@@ -1043,7 +1043,7 @@ def construct_checkpoint(self) -> bool:
                 project.storage.geodiff.concat_changes(diffs_paths, self.abs_path)
         except (GeoDiffLibError, GeoDiffLibConflictError):
             logging.error(
-                f"Geodiff: Failed to merge diffs for file {self.file_path_id}. Diffs: {diffs_paths}"
+                f"Geodiff: Failed to merge diffs for file {self.file_path_id}."
             )
             return False