Fixed NPE

src/main/java/de/svenkubiak/jpushover/JPushover.java

@@ -378,7 +378,7 @@ public class JPushover {
             LOG.error("Failed to send message to pushover", e);
         }
         
-        return null;
+        return jPushoverResponse;
     }
 
     public String getToken() {

src/test/java/de/svenkubiak/jpushover/TestJPushover.java

@@ -73,5 +73,8 @@ public class TestJPushover {
         File file = new File(UUID.randomUUID().toString());
         push.withAttachment(file);
         assertTrue(push.getAttachment() != null);
+        
+        JPushoverResponse response = push.push();
+        assertTrue(response != null);
     }
 }