[BUG] Flash\Session output() throws exception when session is empty

[zsilbi]

Actual Behavior

Flash is initialized in bootstrap.

$di->set('flashSession', function () {
   return new \Phalcon\Flash\Session();
});

In index.volt

<div id="flash-messages">{{ flashSession.output() }}</div>

Result when there are no messages:

phalcon/Flash/Session.zep:90: [Exception] The argument is not initialized or iterable()

Expected behavior would be an empty output.

Details

• Phalcon version: 4.0.0-alpha.4
• PHP Version: 7.2.16 and 7.3.4
• Operating System: Ubuntu 16.04
• Installation type: Compiling from source
• Zephir version (if any): Version 0.11.12
• Server: nginx
• Other related info (Database, table schema): MariaDB 10.1.37

[niden]

Addressed in: #14024