@staticmethod
def _get_wwn(controllerport):
    """Return the WWN value of the controller port.

        Usually the WWN key in the controller port is wwn or WWN, but there
        are cases where the backend returns wWW, so we have to check all the
        keys.
        """
    for key, value in controllerport.items():
        if key.lower() == 'wwn':
            return value
    return None
