@Override
    public StrCatFunction copy() {
        return new StrCatFunction(getLabel(),
                                  getLevelOrNull(),
                                  args().stream().map(arg -> arg.copy()).toList());
    }
Constructs a new instance of this class.

@param arg1 The first compulsory argument, must evaluate to a string.
@param arg2 The second compulsory argument, must evaluate to a string.
@param argN The optional arguments, must evaluate to a string.
container-search/src/main/java/com/yahoo/search/grouping/request/StrCatFunction.java