private void addItems(OperatorNode<ExpressionOperator> ast, WeightedSetItem out) {
        switch (ast.getOperator()) {
            case MAP -> addStringItems(ast, out);
            case ARRAY -> addLongItems(ast, out);
            case VARREF -> {
                Preconditions.checkState(userQuery != null, "Query properties are not available");
                ParameterListParser.addItemsFromString(userQuery.properties().getString(ast.getArgument(0, String.class)), out);
            }
            default -> throw newUnexpectedArgumentException(ast.getOperator(),
                                                            ExpressionOperator.ARRAY, ExpressionOperator.MAP);
        }
    }
The sorting specified in the YQL+ query last parsed.

@return a Sorting instance or null
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java