public ResultBuilder setRequestId(int requestId) {
        root = new RootGroup(requestId, continuation);
        rootBuilder = new GroupListBuilder(ResultId.valueOf(requestId), 0, true, true);
        return this;
    }
Sets the id of the {@link GroupingRequest} that this builder is creating the result for.

@param requestId the id of the corresponding GroupingRequest
@return this, to allow chaining
container-search/src/main/java/com/yahoo/search/grouping/vespa/ResultBuilder.java