def _split_alleles(allele_ids: bytes) -> List[bytes]:
    alleles = allele_ids.split(b',')
    if (len(alleles) != 2):
        raise NotImplementedError(f"Bgen reads only supported for biallelic variants (found non-biallelic variant '{str(allele_ids)}')")
    return alleles
def _split_alleles(allele_ids: bytes) -> List[bytes]:
    alleles = allele_ids.split(b',')
    if (len(alleles) != 2):
        raise NotImplementedError(f"Bgen reads only supported for biallelic variants (found non-biallelic variant '{str(allele_ids)}')")
    return alleles