private static Expression<?> merge(Expression<?>... args) {
        if (args.length == 1) {
            return args[0];
        } else {
            return ExpressionUtils.list(Object.class, args);
        }
    }
{@code WithinGroup} is a builder for {@code WITHIN GROUP} constructs

@param <T> expression type

@author tiwe
querydsl-sql/src/main/java/com/querydsl/sql/WithinGroup.java