code: def test_null_property_encoding():
      """A null feature property is retained."""
      # Verifies fix for gh-1270.
      assert ObjectEncoder().default(Properties(a=1, b=None)) == {
          "a": 1,
          "b": None,
      }
  
imports: import pytest
  from fiona.errors import FionaDeprecationWarning
  from fiona.model import _Geometry, Feature, Geometry, Object, ObjectEncoder, Properties, decode_object
label_desc: Use image node_id 31 for calling a global function with example usage: test_null_property_encoding() without return types