input: Write a function to replace empty cells with the median value of the column in a pandas DataFrame.
  assert replace_empty_with_median(pd.DataFrame({'A': [1, 2, None, 4], 'B': [None, 2, 3, 4]})).equals(pd.DataFrame({'A': [1, 2, 2.5, 4], 'B': [3, 2, 3, 4]}))
  assert replace_empty_with_median(pd.DataFrame({'A': [None, None, None, None], 'B': [1, 1, 1, 1]})).equals(pd.DataFrame({'A': [None, None, None, None], 'B': [1, 1, 1, 1]}))
  assert replace_empty_with_median(pd.DataFrame({'A': [1, 2, 3], 'B': [None, None, None]})).equals(pd.DataFrame({'A': [1, 2, 3], 'B': [None, None, None]}))
output: import pandas as pd
  import numpy as np
  
  def replace_empty_with_median(df):
      for column in df.columns:
          if df[column].isnull().all():
              continue
          median_value = df[column].median()
          df[column].fillna(median_value, inplace=True)
      return df