/**
* Performs the fail function.
*
* @param ctx query context
* @return resulting value
* @throws QueryException query exception
*/
private Item fail(final QueryContext ctx) throws QueryException {
throw UNIT_MESSAGE.thrw(info, checkStr(expr[0], ctx));
}
/**
* Performs the assert function.
*
* @param ctx query context
* @return resulting value
* @throws QueryException query exception
*/
private Item assrt(final QueryContext ctx) throws QueryException {
final byte[] str = expr.length < 2 ? null : checkStr(expr[1], ctx);
if (expr[0].ebv(ctx, info).bool(info)) return null;
throw str == null ? UNIT_ASSERT.thrw(info) : UNIT_MESSAGE.thrw(info, str);
}