private Item fetchUserQuery() {
        Preconditions.checkState(!queryParser, "Tried inserting user query into itself.");
        Preconditions.checkState(userQuery != null,
                                 "User query must be set before trying to build complete query "
                                 + "tree including user query.");
        return userQuery.getModel().getQueryTree().getRoot();
    }
The YQL query language.

This class <em>must</em> be kept in lockstep with {@link VespaSerializer}.
Adding anything here will usually require a corresponding addition in
VespaSerializer.

@author Steinar Knutsen
@author Stian Kristoffersen
@author Simon Thoresen Hult
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java