Description:
------------
Test code - https://3v4l.org/7bfQS




Test script:
---------------
<?php

class Foo
{
    /**
     * Values
     * @var array
     */
    const VALUES = [
        'key1' => 'value1',
        'key2' => 'value2',
        'key3' => 'value3'
    ];

    /**
     * Test function
     */
    public function execute()
    {
        $key = 'key4';
        if (!empty(self::VALUES[$key])) {
            self::VALUES[$key];
        } else {
            echo 'The key doesn\'t found in this array.';
        }
    }
}

$foo = new Foo();
$foo->execute();

Expected result:
----------------
There should not be E_NOTICE

Actual result:
--------------
I get E_NOTICE