code: public static Expression exists(String operator, Val<Expression>[] args, EbeanExprInvoker invoker) {
          if (args.length == 1) {
              if (args[0].object() instanceof QueryExpression) {
                  return factory(invoker).exists(((QueryExpression<?>) args[0].object()).query);
              }
              throw new QuerySyntaxException(Messages.get("dsl.arguments.error3", operator));
          }
          throw new QuerySyntaxException(Messages.get("dsl.arguments.error0", operator));
      }
docs: <p>exists.</p>
  
  @param operator a {@link java.lang.String} object.
  @param args an array of {@link ameba.db.dsl.QueryExprMeta.Val} objects.
  @param invoker a {@link ameba.db.ebean.filter.EbeanExprInvoker} object.
  @return a {@link io.ebean.Expression} object.