Make the absl::Status type caster convert Python None to OkStatus.

PiperOrigin-RevId: 508428006

pybind11_abseil/status_caster.h

@@ -72,6 +72,11 @@ struct type_caster<absl::Status> : public type_caster_base<absl::Status> {
 
   bool load(handle src, bool convert) {
     if (type_caster_base<absl::Status>::load(src, convert)) {
+      // Behavior change 2023-02-09: previously `value` was simply left as
+      // `nullptr`.
+      if (!value) {
+        value = const_cast<absl::Status*>(pybind11_abseil::OkStatusSingleton());
+      }
       return true;
     }
     if (convert) {

pybind11_abseil/tests/status_example_test.py

@@ -192,11 +192,16 @@ class StatusTest(parameterized.TestCase):
     with self.assertRaises(TypeError):
       status_example.extract_code_message(cap)
 
-  @parameterized.parameters(None, '', 0)
+  @parameterized.parameters('', 0)
   def test_status_caster_load_no_as_absl_status(self, something_random):
     with self.assertRaises(TypeError):
       status_example.extract_code_message(something_random)
 
+  def test_status_caster_load_none(self):
+    code, msg = status_example.extract_code_message(None)
+    self.assertEqual(code, status.StatusCode.OK)
+    self.assertEqual(msg, '')
+
   def test_return_ok_status_return_value_policy_clif_automatic(self):
     self.assertIsNone(status_example.return_ok_status(False))
     if not status_example.PYBIND11_HAS_RETURN_VALUE_POLICY_CLIF_AUTOMATIC: