diff --git a/src/OneSignalMessage.php b/src/OneSignalMessage.php
index 3ba14de..c53201c 100644
--- a/src/OneSignalMessage.php
+++ b/src/OneSignalMessage.php
@@ -185,7 +185,7 @@ public function toArray()
     {
         $message = [
             'contents' => ['en' => $this->body],
-            'headings' => ['en' => $this->subject],
+            'headings' => $this->subjectToArray(),
             'url' => $this->url,
             'buttons' => $this->buttons,
             'web_buttons' => $this->webButtons,
@@ -205,4 +205,13 @@ public function toArray()
 
         return $message;
     }
+
+    protected function subjectToArray()
+    {
+        if ($this->subject === null) {
+            return [];
+        }
+
+        return ['en' => $this->subject];
+    }
 }
diff --git a/tests/MessageTest.php b/tests/MessageTest.php
index 050cf40..5c1ca3d 100644
--- a/tests/MessageTest.php
+++ b/tests/MessageTest.php
@@ -50,6 +50,12 @@ public function it_can_set_the_subject()
         $this->assertEquals('mySubject', Arr::get($this->message->toArray(), 'headings.en'));
     }
 
+    /** @test */
+    public function it_does_not_append_empty_subject_value_when_subject_is_null()
+    {
+        $this->assertEquals([], Arr::get($this->message->toArray(), 'headings'));
+    }
+
     /** @test */
     public function it_can_set_the_url()
     {