fix: dbapi raised AttributeError with [] as arguments (#1257)

If the cursor.execute(sql, args) function was called with an empty array
instead of None, it would raise an AttributeError like this:

AttributeError: 'list' object has no attribute 'items'

This is for example automatically done by SQLAlchemy when executing a
raw statement on a dbapi connection.

google/cloud/spanner_v1/transaction.py

@@ -308,7 +308,7 @@ def _make_params_pb(params, param_types):
         :raises ValueError:
             If ``params`` is None but ``param_types`` is not None.
         """
-        if params is not None:
+        if params:
             return Struct(
                 fields={key: _make_value_pb(value) for key, value in params.items()}
             )

tests/mockserver_tests/test_basics.py

@@ -15,6 +15,8 @@
 import unittest
 
 from google.cloud.spanner_admin_database_v1.types import spanner_database_admin
+from google.cloud.spanner_dbapi import Connection
+from google.cloud.spanner_dbapi.parsed_statement import AutocommitDmlMode
 from google.cloud.spanner_v1.testing.mock_database_admin import DatabaseAdminServicer
 from google.cloud.spanner_v1.testing.mock_spanner import (
     start_mock_server,
@@ -29,6 +31,8 @@
     FixedSizePool,
     BatchCreateSessionsRequest,
     ExecuteSqlRequest,
+    BeginTransactionRequest,
+    TransactionOptions,
 )
 from google.cloud.spanner_v1.database import Database
 from google.cloud.spanner_v1.instance import Instance
@@ -62,6 +66,10 @@ def tearDownClass(cls):
             TestBasics.server.stop(grace=None)
             TestBasics.server = None
 
+    def teardown_method(self, *args, **kwargs):
+        TestBasics.spanner_service.clear_requests()
+        TestBasics.database_admin_service.clear_requests()
+
     def _add_select1_result(self):
         result = result_set.ResultSet(
             dict(
@@ -88,6 +96,19 @@ def _add_select1_result(self):
         result.rows.extend(["1"])
         TestBasics.spanner_service.mock_spanner.add_result("select 1", result)
 
+    def add_update_count(
+        self,
+        sql: str,
+        count: int,
+        dml_mode: AutocommitDmlMode = AutocommitDmlMode.TRANSACTIONAL,
+    ):
+        if dml_mode == AutocommitDmlMode.PARTITIONED_NON_ATOMIC:
+            stats = dict(row_count_lower_bound=count)
+        else:
+            stats = dict(row_count_exact=count)
+        result = result_set.ResultSet(dict(stats=result_set.ResultSetStats(stats)))
+        TestBasics.spanner_service.mock_spanner.add_result(sql, result)
+
     @property
     def client(self) -> Client:
         if self._client is None:
@@ -145,3 +166,27 @@ def test_create_table(self):
         )
         operation = database_admin_api.update_database_ddl(request)
         operation.result(1)
+
+    # TODO: Move this to a separate class once the mock server test setup has
+    #       been re-factored to use a base class for the boiler plate code.
+    def test_dbapi_partitioned_dml(self):
+        sql = "UPDATE singers SET foo='bar' WHERE active = true"
+        self.add_update_count(sql, 100, AutocommitDmlMode.PARTITIONED_NON_ATOMIC)
+        connection = Connection(self.instance, self.database)
+        connection.autocommit = True
+        connection.set_autocommit_dml_mode(AutocommitDmlMode.PARTITIONED_NON_ATOMIC)
+        with connection.cursor() as cursor:
+            # Note: SQLAlchemy uses [] as the list of parameters for statements
+            # with no parameters.
+            cursor.execute(sql, [])
+            self.assertEqual(100, cursor.rowcount)
+
+        requests = self.spanner_service.requests
+        self.assertEqual(3, len(requests), msg=requests)
+        self.assertTrue(isinstance(requests[0], BatchCreateSessionsRequest))
+        self.assertTrue(isinstance(requests[1], BeginTransactionRequest))
+        self.assertTrue(isinstance(requests[2], ExecuteSqlRequest))
+        begin_request: BeginTransactionRequest = requests[1]
+        self.assertEqual(
+            TransactionOptions(dict(partitioned_dml={})), begin_request.options
+        )