code: def null_df(rng, long_df):
      df = long_df.copy()
      for col in df:
          if pd.api.types.is_integer_dtype(df[col]):
              df[col] = df[col].astype(float)
          idx = rng.permutation(df.index)[:10]
          df.loc[idx, col] = np.nan
      return df
  
imports: import numpy
  import pandas
  import pytest
label_desc: Use image node_id 19 for calling a global function with example usage: null_df(rng, long_df) and returns: df