code: def test_midpoint_nan():
      all_nan = pd.Series([(np.nan, np.nan), (np.nan, np.nan)])
      latlong1 = pd.Series([(0, 0), (0, 0)])
      function = GeoMidpoint().get_function()
      answer = function(all_nan, latlong1)
      for lat, longi in answer:
          assert np.isnan(lat)
          assert np.isnan(longi)
  
file_path: featuretools/featuretools/tests/primitive_tests/transform_primitive_tests/test_latlong_primitives.py
imports: import numpy
  import pandas
  import pytest
  from featuretools.primitives import CityblockDistance, GeoMidpoint, IsInGeoBox
label_desc: Use image node_id 7 for calling a global function with example usage: test_midpoint_nan() without return types