sync ignores objects missing on the *source* side

We don't support deletion of objects yet.
So, skip if the object is not present on the *source* side.

packages/syft/src/syft/service/sync/diff_state.py

@@ -1215,6 +1215,12 @@ def from_sync_state(
                 low_status = "NEW"
                 high_status = "NEW"
 
+            # We don't support deletion of objects yet.
+            # So, skip if the object is not present on the *source* side
+            source_obj = low_obj if direction == SyncDirection.LOW_TO_HIGH else high_obj
+            if source_obj is None:
+                continue
+
             diff = ObjectDiff.from_objects(
                 low_obj=low_obj,
                 high_obj=high_obj,

packages/syft/tests/syft/service/sync/sync_resolve_single_test.py

@@ -136,6 +136,20 @@ def compute() -> int:
     assert res == compute(syft_no_server=True)
 
 
+def test_skip_deletion(low_worker, high_worker):
+    low_client: DatasiteClient = low_worker.root_client
+    high_client: DatasiteClient = high_worker.root_client
+
+    @sy.syft_function_single_use()
+    def compute() -> int:
+        return 42
+
+    _ = low_client.code.request_code_execution(compute)
+
+    w = sy.sync(high_client, low_client)
+    assert isinstance(w, SyftSuccess), f"Expected empty diff, got {w}"
+
+
 def test_diff_state_with_dataset(low_worker: Worker, high_worker: Worker):
     low_client: DatasiteClient = low_worker.root_client
     client_low_ds = get_ds_client(low_client)