Add a missing @skip_postgresql

Author: schlatterbeck

test/test_indexer.py

@@ -734,6 +734,7 @@ def test_query_errors(self):
         error = 'Query error: syntax error near "^"'
         self.assertEqual(str(ctx.exception), error)
 
+    @skip_postgresql
     def testNullChar(self):
        """Test with null char in string. FTS will throw
           an error on null.