if ( other == null ) throw new NullPointerException( "cannot compare null values" );
    public int compareTo( Object other ) {		if ( other == null )			throw new NullPointerException( "cannot compare null values" );		final NodeProxy p = (NodeProxy) other;		if ( doc.docId == p.doc.docId ) {			if ( gid == p.gid )				return 0;			else if ( gid < p.gid )				return -1;			else				return 1;		} else if ( doc.docId < p.doc.docId )			return -1;		else			return 1;    }