Fix bug gcloud-datastore will raise exception while attemping to save…

… property

values set as empty list.

gcloud/datastore/connection.py

@@ -433,6 +433,10 @@ def save_entity(self, dataset_id, key_pb, properties,
            will be replaced by those passed in 'properties';  properties
            not passed in 'properties' no longer be set for the entity.
 
+        .. note::
+           When saving an entity to the backend, property values set as
+           empty lists or None cannot be saved and will be ignored.
+
         :type dataset_id: string
         :param dataset_id: The dataset in which to save the entity.
 
@@ -460,6 +464,9 @@ def save_entity(self, dataset_id, key_pb, properties,
         insert.key.CopyFrom(key_pb)
 
         for name, value in properties.items():
+            if isinstance(value, list) and len(value) == 0:
+                continue
+
             prop = insert.property.add()
             # Set the name of the property.
             prop.name = name

gcloud/datastore/test_connection.py

@@ -917,6 +917,42 @@ def test_allocate_ids_non_empty(self):
         request.ParseFromString(cw['body'])
         self.assertEqual(list(request.key), before_key_pbs)
 
+    def test_save_entity_w_empty_list(self):
+        from gcloud.datastore.connection import datastore_pb
+        from gcloud.datastore.key import Key
+
+        DATASET_ID = 'DATASET'
+        key_pb = Key(path=[{'kind': 'Kind', 'id': 1234}]).to_protobuf()
+        rsp_pb = datastore_pb.CommitResponse()
+        conn = self._makeOne()
+        URI = '/'.join([
+            conn.API_BASE_URL,
+            'datastore',
+            conn.API_VERSION,
+            'datasets',
+            DATASET_ID,
+            'commit',
+        ])
+        http = conn._http = Http({'status': '200'}, rsp_pb.SerializeToString())
+        result = conn.save_entity(DATASET_ID, key_pb,
+                                  {'foo': u'Foo', 'bar': []})
+        self.assertEqual(result, True)
+        cw = http._called_with
+        self._verifyProtobufCall(cw, URI, conn)
+        rq_class = datastore_pb.CommitRequest
+        request = rq_class()
+        request.ParseFromString(cw['body'])
+        self.assertEqual(request.transaction, '')
+        mutation = request.mutation
+        self.assertEqual(len(mutation.insert_auto_id), 0)
+        upserts = list(mutation.upsert)
+        self.assertEqual(len(upserts), 1)
+        upsert = upserts[0]
+        self.assertEqual(upsert.key, key_pb)
+        props = list(upsert.property)
+        self.assertEqual(len(props), 1)
+        self.assertNotEqual(props[0].name, 'bar')
+
     def test_save_entity_wo_transaction_w_upsert(self):
         from gcloud.datastore.connection import datastore_pb
         from gcloud.datastore.key import Key