Utility function to determine fill values for variants fields with
    missing values.

def _variants_fills(fields, fills, info_types):
    """Utility function to determine fill values for variants fields with
    missing values."""
    if fills is None:
        # no fills specified by user
        fills = dict()
    for f, vcf_type in zip(fields, info_types):
        if f == 'FILTER':
            fills[f] = False
        elif f not in fills:
            if f in config.STANDARD_VARIANT_FIELDS:
                fills[f] = config.DEFAULT_VARIANT_FILL[f]
            else:
                fills[f] = config.DEFAULT_FILL_MAP[vcf_type]
    # convert to tuple for zipping with fields
    fills = tuple(fills[f] for f in fields)
    return fills