private List<String> toGroupingRequests(String groupingJson) {
        Inspector inspector = SlimeUtils.jsonToSlime(groupingJson).get();
        if (inspector.field("error_message").valid()) {
            throw new IllegalInputException("Illegal query: " + inspector.field("error_message").asString() +
                                            " at: '" + new String(inspector.field("offending_input").asData(), StandardCharsets.UTF_8) + "'");
        }

        List<String> operations = new ArrayList<>();
        inspector.traverse((ArrayTraverser) (__, item) -> operations.add(toGroupingRequest(item)));
        return operations;
    }
Translates a list of grouping requests on JSON form to a list in the grouping language form
container-search/src/main/java/com/yahoo/search/query/SelectParser.java