code: def test_nulls(fill_df):
      """
      Test output if nulls are present
      """
      actual = fill_df.complete(["value1"], "value2", sort=True)
      ind = [fill_df.value1.dropna().unique(), fill_df.value2.unique()]
      ind = pd.MultiIndex.from_product(ind, names=["value1", "value2"])
      ind = pd.DataFrame([], index=ind)
      expected = fill_df.merge(
          ind, on=["value1", "value2"], how="outer", sort=True
      )
      assert_frame_equal(actual, expected)
  
imports: from string import ascii_lowercase
  import numpy
  import pandas
  import pytest
  from hypothesis import given, settings
  from pandas.testing import assert_frame_equal
  from janitor.testing_utils.strategies import categoricaldf_strategy
label_desc: Use image node_id 37 for calling a global function with example usage: test_nulls(fill_df) without return types