code: def test_is_none_works(self) -> None:
      self.card.field("field7").set(None)
  
      assert self.card.field("field7").is_none()
  
      self.card.field("field2").field("sub_field1").set(None)
  
      assert self.card.field("field2").field("sub_field1").is_none()
  
imports: from os import PathLike
  from pathlib import Path
  import pytest
  from fairseq2.assets import AssetCard, AssetCardError, AssetCardFieldNotFoundError
label_desc: Use image node_id 3 for calling the TestAssetCard obj's underlying member method code with example usage: obj.test_is_none_works() without return types