public Long append( Long s1, Long s2 )
    {
        if ( s1 == null || s2 == null )
        {
            return null;
        }
        return s1 + s2;
    }
public Long append ( Long s1 , Long s2 ) { if ( s1 == null || s2 == null ) { return null ; } return s1 + s2 ; }
{@inheritDoc}