def get_gap(numberlist: list):
    """Get gap

    Can take an integer list returned by :meth:`get_numbers` and determine
    the missing sequence number.

    Args:
        numberlist: List of numbers to find a gap in.

    Returns:
        Missing number in the sequence or None if there is no gap.
    """
    seqlist = list(range(numberlist[0], numberlist[-1] + 1))
    for element in seqlist:
        if element not in numberlist:
            return element
    return None