Add new NullToken, to satisfy type hint checks when token would otherwise not be set.

src/GaryJones/OAuth/NullToken.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * OAuth
+ *
+ * @package OAuth
+ * @author Andy Smith
+ * @author Gary Jones <gary@garyjones.co.uk>
+ * @license https://raw.github.com/GaryJones/OAuth/master/LICENSE MIT
+ * @link https://github.com/GaryJones/OAuth
+ */
+
+namespace GaryJones\OAuth;
+
+/**
+ * Token holds the properties of a single token.
+ *
+ * This class deals with both temporary (request) and token (access) credntials.
+ *
+ * @package OAuth
+ * @author Gary Jones <gary@garyjones.co.uk>
+ */
+class NullToken extends Token
+{
+    /**
+     * Constructs a new client object and populates the required parameters.
+     *
+     * @param string $key    Client key / identifier.
+     * @param string $secret Client shared-secret.
+     */
+    public function __construct()
+    {
+        $this->setKey('');
+        $this->setSecret('');
+    }
+}

src/GaryJones/OAuth/Server.php

@@ -88,7 +88,7 @@ class Server
         $client = $this->getClient($request);
 
         // no token required for the initial token request
-        $token = null;
+        $token = new NullToken;
 
         $this->checkSignature($request, $client, $token);