def convert_role_id (role):
    """
    Convert a user role parameter to the string that needs to be passed to system functions.
    
    :param role: The role parameter passed to the command.  If this is None, no conversion is
    performed.
    
    :return The string identifier for the role.  This will be empty if the role parameter is not
    valid.
    """
    
    if (role is not None):
        if ((role == "0") or (role == "wcscmuser")):
            role = "user"
        elif ((role == "1") or (role == "wcscmoperator")):
            role = "operator"
        elif ((role == "2") or (role == "wcscmadmin")):
            role = "admin"
        else:
            role = ""
        
    return role