Unable to Use "Null" Broadcast Driver

[mcordingley]

• Laravel Version: 5.7.20
• PHP Version: 7.3
• Database Driver & Version: N/A

Description:

"Null" is described in the documentation as a valid broadcast driver. However, setting BROADCAST_DRIVER to be null, "null", or empty does not actually select the null driver. Essentially, this is a repeat of #11051 in a new context.

Steps To Reproduce:

1. Uncomment App\Providers\BroadcastServiceProvider::class, in config/app.php.
2. Set BROADCAST_DRIVER=null in .env.
3. Attempt to load a page to trigger an error.

[mcordingley]

Dang, that was fast!