Fix for expected params on tts callback.

Author: tjlytle

src/Nexmo/Voice/Message/Callback.php

@@ -20,8 +20,6 @@ class Callback extends BaseCallback implements CallbackInterface
         'to',
         'call-request',
         'network-code',
-        'call-start',
-        'call-end'
     );
 
     public function getId()
@@ -61,11 +59,19 @@ public function getCreated()
 
     public function getStart()
     {
+        if(!isset($this->data['call-start'])){
+            return null;
+        }
+
         return \DateTime::createFromFormat(self::TIME_FORMAT, $this->data['call-start']);
     }
 
     public function getEnd()
     {
+        if(!isset($this->data['call-end'])){
+            return null;
+        }
+
         return \DateTime::createFromFormat(self::TIME_FORMAT, $this->data['call-end']);
     }
 

tests/Nexmo/Voice/Message/CallbackTest.php

@@ -39,6 +39,16 @@ public function testSimpleValues()
         $this->assertEquals($this->data['to'], $this->callback->getTo());
         $this->assertEquals($this->data['network-code'], $this->callback->getNetwork());
     }
+    public function testStartAndEndOptional()
+    {
+        unset($this->data['call-start']);
+        unset($this->data['call-end']);
+
+        $this->callback = new Callback($this->data);
+
+        $this->assertNull($this->callback->getStart());
+        $this->assertNull($this->callback->getEnd());
+    }
 
     public function testDateValues()
     {