Provide default message on PR decline.

When a PR is declined without a `message` parameter, add an empty
message to the payload.

Fix & close #43

Author: vimishor

lib/Bitbucket/API/Repositories/PullRequests.php

@@ -309,6 +309,10 @@ public function accept($account, $repo, $id, $params = array())
      */
     public function decline($account, $repo, $id, $params = array())
     {
+        if (false === array_key_exists('message', $params)) {
+            $params['message'] = '';
+        }
+
         return $this->getClient()->setApiVersion('2.0')->post(
             sprintf('repositories/%s/%s/pullrequests/%d/decline', $account, $repo, $id),
             json_encode($params),

test/Bitbucket/Tests/API/Repositories/PullRequestsTest.php

@@ -4,6 +4,7 @@
 
 use Bitbucket\Tests\API as Tests;
 use Bitbucket\API;
+use Buzz\Message\RequestInterface;
 
 /**
  * Class PullRequestsTest
@@ -318,4 +319,25 @@ public function testDeclineAPullRequest()
 
         $pull->decline('gentle', 'eof', 1, $params);
     }
+
+    /**
+     * @ticket 43
+     */
+    public function testDeclineAPullRequestWithoutAMessage()
+    {
+        $endpoint   = 'repositories/gentle/eof/pullrequests/1/decline';
+        $params     = array(
+            'message' => ''
+        );
+
+        $client = $this->getHttpClientMock();
+        $client->expects($this->once())
+            ->method('post')
+            ->with($endpoint, json_encode($params));
+
+        /** @var \Bitbucket\API\Repositories\PullRequests $pull */
+        $pull   = $this->getClassMock('Bitbucket\API\Repositories\PullRequests', $client);
+
+        $pull->decline('gentle', 'eof', 1, array());
+    }
 }