public static List<GroupingOperation> fromStringAsList(String string) {
        if (string == null || string.trim().isEmpty()) {
            return List.of();
        }
        GroupingParserInput input = new GroupingParserInput(string);
        try {
            return new GroupingParser(input).requestList();
        } catch (ParseException | TokenMgrException e) {
            throw new IllegalArgumentException(input.formatException(e.getMessage()), e);
        }
    }
Parses the given string as a list of grouping operations. This method never returns null, it either returns a
list of valid grouping requests or it throws an exception.

@param string the string to parse
@return a list of grouping operations that corresponds to the string
@throws IllegalArgumentException thrown if the string could not be parsed
container-search/src/main/java/com/yahoo/search/grouping/request/GroupingOperation.java