Show a different error message when loading Python None as StatusOr<T>.

PiperOrigin-RevId: 520495543

pybind11_abseil/statusor_caster.h

@@ -50,6 +50,10 @@ struct type_caster<absl::StatusOr<PayloadType>> {
       value = cast_op<PayloadType>(std::move(payload_caster));
       return true;
     }
+    if (src.is_none()) {
+      throw cast_error(
+          "None is not a valid value for a StatusOr<T> argument.");
+    }
     StatusCaster status_caster;
     if (status_caster.load(src, convert)) {
       absl::Status status = cast_op<absl::Status>(std::move(status_caster));

pybind11_abseil/tests/status_example_test.py

@@ -57,7 +57,7 @@ class StatusTest(parameterized.TestCase):
       status_example.check_statusor(None, status.StatusCode.CANCELLED)
     self.assertEqual(
         str(ctx.exception),
-        'An OK status is not a valid constructor argument to StatusOr<T>.')
+        'None is not a valid value for a StatusOr<T> argument.')
 
   def test_return_status_return_type_from_doc(self):
     self.assertEndsWith(