Php versions – Laravel 5.5 won't render email with PHP 7.4

I am trying to render an email in Laravel 5.5, but no matter what I do, I get the following error on render:
ErrorException (E_NOTICE) Trying to access array offset on value of type null

happens in vendoreguliasemail-validatorEmailValidatorParserParser.php

I am running php 7.4 and I believe the error does NOT happen on php 7.3.

web.php:

Route::get('scratch', function(){
  $mail = new Test();
  return $mail->render();
});

Test.php

<?php

namespace AppMail;

use IlluminateBusQueueable;
use IlluminateMailMailable;
use IlluminateQueueSerializesModels;

class Test extends Mailable
{
  use Queueable, SerializesModels;

  public $subscription;

  /**
   * Create a new message instance.
   *
   * @return void
   */
  public function __construct()
  {
  }

  /**
   * Build the message.
   *
   * @return $this
   */
  public function build()
  {
    return $this->view('emails.test');
  }
}

test.blade.php

Hello from world

I’m thinking this has to be an issue with Laravel 5.5 and PHP 7.4. I can change my version but I’d like to avoid that if possible. Upgrading Laravel won’t work for this application.

edit

It’s failing on this line in vendoreguliasemail-validatorEmailValidatorParserParser.php

 protected function escaped()
    {
        $previous = $this->lexer->getPrevious();
 
        if ($previous['type'] === EmailLexer::S_BACKSLASH  // here
            &&
            $this->lexer->token['type'] !== EmailLexer::GENERIC
        ) {
            return true;
        }
 
        return false;
    }