<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def combine_tax_scales(node):
 """ Combine all the MarginalRateTaxScales in the node into a single MarginalRateTaxScale. """

    combined_tax_scales = None
    for child_name in node:
        child = node[child_name]

        if not isinstance(child, AbstractTaxScale):
            log.info('Skipping {} with value {} because it is not a tax scale'.format(child_name, child))
            continue

        if combined_tax_scales is None:
            combined_tax_scales = MarginalRateTaxScale(name = child_name)
            combined_tax_scales.add_bracket(0, 0)
        combined_tax_scales.add_tax_scale(child)
    return combined_tax_scales