diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index a7b5fbd1..f700c57b 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -276,7 +276,9 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function getRequestParameter($parameter, ServerRequestInterface $request, $default = null)
     {
-        return (isset($request->getParsedBody()[$parameter])) ? $request->getParsedBody()[$parameter] : $default;
+        $requestParameters = (array) $request->getParsedBody();
+
+        return isset($requestParameters[$parameter]) ? $requestParameters[$parameter] : $default;
     }
 
     /**
@@ -290,7 +292,7 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function getQueryStringParameter($parameter, ServerRequestInterface $request, $default = null)
     {
-        return (isset($request->getQueryParams()[$parameter])) ? $request->getQueryParams()[$parameter] : $default;
+        return isset($request->getQueryParams()[$parameter]) ? $request->getQueryParams()[$parameter] : $default;
     }
 
     /**
@@ -304,13 +306,13 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function getCookieParameter($parameter, ServerRequestInterface $request, $default = null)
     {
-        return (isset($request->getCookieParams()[$parameter])) ? $request->getCookieParams()[$parameter] : $default;
+        return isset($request->getCookieParams()[$parameter]) ? $request->getCookieParams()[$parameter] : $default;
     }
 
     /**
      * Retrieve server parameter.
      *
-     * @param string|array                             $parameter
+     * @param string                                   $parameter
      * @param \Psr\Http\Message\ServerRequestInterface $request
      * @param mixed                                    $default
      *
@@ -318,7 +320,7 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function getServerParameter($parameter, ServerRequestInterface $request, $default = null)
     {
-        return (isset($request->getServerParams()[$parameter])) ? $request->getServerParams()[$parameter] : $default;
+        return isset($request->getServerParams()[$parameter]) ? $request->getServerParams()[$parameter] : $default;
     }
 
     /**
@@ -440,7 +442,11 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     public function canRespondToRequest(ServerRequestInterface $request)
     {
-        return isset($request->getParsedBody()['grant_type'])
-        && $request->getParsedBody()['grant_type'] === $this->getIdentifier();
+        $requestParameters = (array) $request->getParsedBody();
+
+        return (
+            array_key_exists('grant_type', $requestParameters)
+            && $requestParameters['grant_type'] === $this->getIdentifier()
+        );
     }
 }
diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 3ee979b2..ca54b824 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -289,29 +289,6 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         return $responseType;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function canRespondToRequest(ServerRequestInterface $request)
-    {
-        return
-            (
-                isset($request->getQueryParams()['response_type'])
-                && $request->getQueryParams()['response_type'] === 'code'
-                && isset($request->getQueryParams()['client_id'])
-            ) || (parent::canRespondToRequest($request));
-    }
-
-    /**
-     * Return the grant identifier that can be used in matching up requests.
-     *
-     * @return string
-     */
-    public function getIdentifier()
-    {
-        return 'authorization_code';
-    }
-
     /**
      * {@inheritdoc}
      */
@@ -329,4 +306,28 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
 
         return $this->respondToAccessTokenRequest($request, $responseType, $accessTokenTTL);
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function canRespondToRequest(ServerRequestInterface $request)
+    {
+        return
+            (
+                array_key_exists('response_type', $request->getQueryParams())
+                && $request->getQueryParams()['response_type'] === 'code'
+                && isset($request->getQueryParams()['client_id'])
+            )
+            || parent::canRespondToRequest($request);
+    }
+
+    /**
+     * Return the grant identifier that can be used in matching up requests.
+     *
+     * @return string
+     */
+    public function getIdentifier()
+    {
+        return 'authorization_code';
+    }
 }