def clean_swrel(swrelset):
    """
    Clean a list of software release lookups.

    :param swrelset: List of software releases.
    :type swrelset: set(str)
    """
    for i in swrelset:
        if i != 'SR not in system' and i is not None:
            swrelease = i
            break
    else:
        swrelease = ''
    return swrelease
