public boolean isEmpty() {
        if (cells.isEmpty()) {
            return true;
        }

        for (Map.Entry<String, List<Cell>> entry : cells.entrySet()) {
            if (!entry.getValue().isEmpty()) {
                return false;
            }
        }
        return true;
    }
public boolean isEmpty ( ) { if ( cells . isEmpty ( ) ) { return true ; } for ( Map . Entry < String , List < Cell > > entry : cells . entrySet ( ) ) { if ( ! entry . getValue ( ) . isEmpty ( ) ) { return false ; } } return true ; }
@return true if this object contains no cells.