def get_total_score_column_index(results_table):
    """
    Returns an index to results_table.serialized_results['cols'] where a total sum of all points
    is stored. Returns None if no 'sum' column is found.
    """
    cols = results_table.serialized_results["cols"]
    for i, col in enumerate(cols):
        if col["key"] == "sum":
            return i