private Item buildLiteral(OperatorNode<ExpressionOperator> ast) {
        var literal = ast.getArgument(0);
        if (Boolean.TRUE.equals(literal)) {
            return new TrueItem();
        }
        if (Boolean.FALSE.equals(literal)) {
            return new FalseItem();
        }
        throw newUnexpectedArgumentException(literal, Boolean.FALSE, Boolean.TRUE);
    }
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