TYPO3 Core

When configuring the Database Abstraction Layer as documented in the manual:

'alternativeMySQLdb' => array(
    'type' => 'native',
    'config' => array(
        'username' => 'your_username',
        'password' => 'your_password',
        'host' => 'localhost',
        'database' => 'alternative_database_name',
    )
),

the database connection will fail, because of the following lines in typo3/sysext/dbal/Classes/Database/DatabaseConnection.php

$link = mysqli_init();
$connected = $link->real_connect(
    $host,
    $cfgArray['config']['username'],
    $cfgArray['config']['password'],
    $cfgArray['config']['database'],
    isset($cfgArray['config']['port']) ? $cfgArray['config']['port'] : ''
);
if ($connected) {

When no portnumber is given, dbal replaces the parameter with an empty string instead of NULL.
Using an empty string produces a php warning:

Warning: mysqli::real_connect() expects parameter 5 to be long, string given

So the line should be changed to:

isset($cfgArray['config']['port']) ? $cfgArray['config']['port'] : NULL

The Bug applies at least to TYPO3 6.2 and 7.6.