Ensure plain text emails don't throw exceptions

src/Mailer.php

@@ -27,11 +27,16 @@ public function send($view, array $data = [], $callback = null)
     protected function applyDebugHeaders(Mailable $mailable)
     {
         $mailable->withSwiftMessage(function (\Swift_Message $swiftMessage) use ($mailable) {
+            $viewFile = $view = $viewContent = $viewData = null;
+
             $viewFile = $this->getMailableViewFile($mailable);
-            $view = $this->getMailableView($viewFile);
-            $viewContent = $this->getMailableViewContent($view);
 
-            $viewData = $this->getMailableViewData($mailable);
+            if (! is_null($viewFile)) {
+                $view = $this->getMailableView($viewFile);
+                $viewContent = $this->getMailableViewContent($view);
+                $viewData = $this->getMailableViewData($mailable);
+            }
+
 
             /**
              * We need to base64 encode the data, as the SMTP header mime encoding could add unwanted

src/TestMail.php

@@ -6,9 +6,17 @@
 
 class TestMail extends Mailable
 {
+    protected $plainText;
+
+    public function __construct($plainText = false)
+    {
+        $this->plainText = $plainText;
+    }
+
     public function build()
     {
-        return $this->subject("Test from HELO")
-            ->markdown('helo::email');
+        $this->subject("Test from HELO");
+
+        return $this->plainText ? $this->text('helo::email') : $this->markdown('helo::email');
     }
 }

tests/HeloTest.php

@@ -29,6 +29,16 @@ public function test_the_mail_commands_sends_the_mailable()
         Mail::assertSent(TestMail::class);
     }
 
+    /** @test */
+    public function test_plain_text_mails_work_correctly()
+    {
+        Mail::fake();
+
+        Mail::to('test@usehelo.com')->send(new TestMail(true));
+
+        Mail::assertSent(TestMail::class);
+    }
+
     /** @test */
     public function test_the_correct_mailer_is_binded()
     {