@Override
    public GroupingExpression setLabel(String label) {
        super.setLabel(label);
        return this;
    }
Returns a string representation of an object that can be used in the 'image' constructor argument of {@link
GroupingNode}. This method ensures that strings are quoted, and that all complex characters are escaped.

@param obj The object to output.
@return The string representation.
container-search/src/main/java/com/yahoo/search/grouping/request/GroupingExpression.java