def get_list(value):
    """Check and convert given value to a set, if required

    >>> from pyams_zfiles.search import get_list
    >>> get_list(None) is None
    True
    >>> get_list('') is None
    True
    >>> get_list('value1;value2')
    ['value1', 'value2']
    """
    if value and isinstance(value, str):
        value = list(map(str.strip, value.split(';')))
    return value or None