public void visit(LiteralNode node) {
        if (state == null ) return;
        if (!(node.getValue() instanceof Long)) {
            throw new IllegalArgumentException("Literal " + node + " is not supported");
        }
    }
Class which converts a selection tree into a set of queries per document type.
If unsupported operations are or illegal arguments are encountered, an exception is thrown.

@author Ulf Lilleengen
document/src/main/java/com/yahoo/document/select/convert/SelectionExpressionConverter.java