def prevent_bad_replacement(overrides_dict, df):
    """Checks that there is not any values equal to the placeholder-values which are used 
        as keys in the overrides dict. If they did exist, this would cause a bad replacement.
        It is very unlikely that this is needed, but just here as an extra safety step"""
    place_holder_values = ['FILL_NA', 'OldValue1', 'OldValue2', 'OldValue3', 'to']
    results_dict = {}
    for search_value in place_holder_values:
        if search_value in df.values:
            results_dict[search_value] = True
            raise Exception(f"Value {search_value} has been found in the dataframe")
    return None