Ignore empty batches instead of sending invalid CQL to Cassandra.

cqlengine/query.py

@@ -169,6 +169,10 @@ class BatchQuery(object):
         self.queries.append((query, params))
 
     def execute(self):
+        if len(self.queries) == 0:
+            # Empty batch is a no-op
+            return
+
         opener = 'BEGIN ' + (self.batch_type + ' ' if self.batch_type else '') + ' BATCH'
         if self.timestamp:
             epoch = datetime(1970, 1, 1)

cqlengine/tests/test_batch_query.py

@@ -103,3 +103,9 @@ class BatchQueryTests(BaseCassEngTestCase):
         for m in TestMultiKeyModel.all():
             m.delete()
 
+    def test_empty_batch(self):
+        b = BatchQuery()
+        b.execute()
+
+        with BatchQuery() as b:
+            pass