def addBucket( main, egressPort="" ):
    """
    Description:
         Create a single bucket which can be added to a Group.
    Optional:
         * egressPort: port of egress device
    Returns:
         * Returns a Bucket
         * Returns None in case of error
    Note:
         The ip and port option are for the requests input's ip and port
         of the ONOS node.
    """
    try:

        bucket = {
                     "treatment": { "instructions": [] }
                 }
        if egressPort:
            bucket[ 'treatment' ][ 'instructions' ].append( {
                                                     "type": "OUTPUT",
                                                     "port": egressPort } )
        return bucket

    except ( AttributeError, TypeError ):
        main.log.exception( self.name + ": Object not as expected" )
        return None
    except Exception:
        main.log.exception( self.name + ": Uncaught exception!" )
        main.cleanup()
        main.exit()