class_docstr: Test ability to marshall selectbox protos.
docstr: Test that it can be called with None as index value.
docstr_tok: ["Test","that","it","can","be","called","with","None","as","index","value","."]
code: def test_none_index(self):
      """Test that it can be called with None as index value."""
      st.selectbox("the label", ("m", "f"), index=None)
  
      c = self.get_delta_from_queue().new_element.selectbox
      self.assertEqual(c.label, "the label")
      # If a proto property is null is not determined by this value,
      # but by the check via the HasField method:
      self.assertEqual(c.default, 0)
      self.assertEqual(c.HasField("default"), False)
  
imports: from unittest.mock import MagicMock, patch
  import numpy
  import pandas
  import pytest
  from parameterized import parameterized
  import streamlit
  from streamlit.errors import StreamlitAPIException
  from streamlit.proto.LabelVisibilityMessage_pb2 import LabelVisibilityMessage
  from streamlit.testing.v1.app_test import AppTest
  from streamlit.testing.v1.util import patch_config_options
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 4 for calling the SelectboxTest obj's underlying member method code with example usage: obj.test_none_index() without return types