fix: handle null values in array query parameters (#426)

Author: HemangChothani

google/cloud/bigquery/_helpers.py

@@ -40,7 +40,7 @@
 
 def _not_null(value, field):
     """Check whether 'value' should be coerced to 'field' type."""
-    return value is not None or field.mode != "NULLABLE"
+    return value is not None or (field is not None and field.mode != "NULLABLE")
 
 
 def _int_from_json(value, field):

tests/unit/test_query.py

@@ -383,6 +383,16 @@ def test_from_api_repr_wo_values(self):
         self.assertEqual(param.array_type, "INT64")
         self.assertEqual(param.values, [])
 
+    def test_from_api_repr_w_none_values(self):
+        RESOURCE = {
+            "parameterType": {"type": "ARRAY", "arrayType": {"type": "INT64"}},
+            "parameterValue": {"arrayValues": [{"value": "1"}, {"value": None}]},
+        }
+        klass = self._get_target_class()
+        param = klass.from_api_repr(RESOURCE)
+        self.assertEqual(param.array_type, "INT64")
+        self.assertEqual(param.values, [1, None])
+
     def test_from_api_repr_w_struct_type(self):
         from google.cloud.bigquery.query import StructQueryParameter