fix(dbapi): avoid running % format with no query parameters (#348)

* fix: aviod running %format when no query params

* fix: nit

* fix: change in unit test

Author: HemangChothani

google/cloud/bigquery/dbapi/cursor.py

@@ -441,7 +441,7 @@ def _format_operation(operation, parameters=None):
             if a parameter used in the operation is not found in the
             ``parameters`` argument.
     """
-    if parameters is None:
+    if parameters is None or len(parameters) == 0:
         return operation
 
     if isinstance(parameters, collections_abc.Mapping):

tests/unit/test_dbapi_cursor.py

@@ -601,3 +601,9 @@ def test__format_operation_w_too_short_sequence(self):
             "SELECT %s, %s;",
             ("hello",),
         )
+
+    def test__format_operation_w_empty_dict(self):
+        from google.cloud.bigquery.dbapi import cursor
+
+        formatted_operation = cursor._format_operation("SELECT '%f'", {})
+        self.assertEqual(formatted_operation, "SELECT '%f'")