code: def test_fill_empty(null_df):
      df = null_df.fill_empty(column_names=["2"], value=3)
      assert set(df.loc[:, "2"]) == set([3])
  
imports: import pandas
  import pytest
label_desc: Use image node_id 1 for calling a global function with example usage: test_fill_empty(null_df) without return types