code: def test_feature_null_field(tmpdir, driver, extension):
      """
      In GDAL 2.2 the behaviour of OGR_F_IsFieldSet slightly changed. Some drivers
      (e.g. GeoJSON) also require fields to be explicitly set to null.
      See GH #460.
      """
      meta = {
          "driver": driver,
          "schema": {
              "geometry": "Point",
              "properties": {"RETURN_P": "str"},
          },
      }
      filename = os.path.join(str(tmpdir), "test_null." + extension)
      with fiona.open(filename, "w", **meta) as dst:
          g = {"coordinates": [1.0, 2.0], "type": "Point"}
          feature = Feature.from_dict(
              **{"geometry": g, "properties": {"RETURN_P": None}}
          )
          dst.write(feature)
  
      with fiona.open(filename, "r") as src:
          feature = next(iter(src))
          assert feature.properties["RETURN_P"] is None
  
imports: import logging
  import os
  import shutil
  import sys
  import tempfile
  import unittest
  import pytest
  import fiona
  from fiona import collection
  from fiona.collection import Collection
  from fiona.model import Feature
  from fiona.ogrext import featureRT
label_desc: Use image node_id 1 for calling a global function with example usage: test_feature_null_field(tmpdir, driver, extension) without return types