def fill_gaps(df, gap_filler_dict):
    """
    Given a Pandas dataframe and a dictionary containing the column names
    the correct 'fillers' for each column, this function will fill
    each column with the correct values when empty cells are found.
        Parameters:
            pd_df (pd.Dataframe): the variable to which the dataframe 
                containing the csv data is assigned
            gap_filler_dict (dict): a dictionary with column name and value 
                to fill gaps as key value pairs, e.g.
                {"Age":"All","Sex":"T"}
        Returns:
            pd.Dataframe: A dataframe with all cells full"""
    df = df.fillna(gap_filler_dict, axis=1)
    return df