Call to a member function has() on null in Drupal\Core\Mail\Plugin\Mail\PhpMail->mail()

Problem/Motivation

Error: Call to a member function has() on null in Drupal\Core\Mail\Plugin\Mail\PhpMail->mail() (line 114 of core/lib/Drupal/Core/Mail/Plugin/Mail/PhpMail.php).
Drupal\mailsystem\Adapter->mail(Array) (Line: 307)
Drupal\Core\Mail\MailManager->doMail('reroute_email', 'test_email_form', 'reniersediego@prometsource.com', 'en', Array, NULL, 1) (Line: 180)
Drupal\Core\Mail\MailManager->Drupal\Core\Mail\{closure}() (Line: 583)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 181)
Drupal\Core\Mail\MailManager->mail('reroute_email', 'test_email_form', 'reniersediego@prometsource.com', 'en', Array, NULL, 1) (Line: 70)
Drupal\mailsystem\MailsystemManager->mail('reroute_email', 'test_email_form', 'reniersediego@prometsource.com', 'en', Array) (Line: 191)
marquettelaw_custom_form_alter(Array, Object, 'reroute_email_test_email_form') (Line: 545)
Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'reroute_email_test_email_form') (Line: 840)
Drupal\Core\Form\FormBuilder->prepareForm('reroute_email_test_email_form', Array, Object) (Line: 284)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 73)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 583)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 166)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 74)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 704)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Run

\Drupal::service('plugin.manager.mail')->mail('reroute_email', 'test_email_form', 'reniersediego@prometsource.com', 'en',
    [
      'cc' => '',
      'bcc'=> '',
      'subject' => 'test',
      'body' => 'test'
    ]);

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet