diff --git a/Slim/Middleware/MethodOverrideMiddleware.php b/Slim/Middleware/MethodOverrideMiddleware.php
index a298bc495..c00a8748f 100644
--- a/Slim/Middleware/MethodOverrideMiddleware.php
+++ b/Slim/Middleware/MethodOverrideMiddleware.php
@@ -39,7 +39,7 @@ public function __invoke(
         } elseif (strtoupper($request->getMethod()) == 'POST') {
             $body = $request->getParsedBody();
 
-            if (!empty($body['_METHOD'])) {
+            if ((is_array($body) || $body instanceof \ArrayAccess) && !empty($body['_METHOD'])) {
                 $request = $request->withMethod($body['_METHOD']);
             }
 
diff --git a/Slim/Router.php b/Slim/Router.php
index 89e58fc44..83ba66540 100644
--- a/Slim/Router.php
+++ b/Slim/Router.php
@@ -419,7 +419,10 @@ public function relativePathFor(string $name, array $data = [], array $queryPara
         }
 
         if (empty($segments)) {
-            throw new InvalidArgumentException('Missing data for URL segment: ' . $segmentName);
+            if (isset($segmentName)) {
+                throw new InvalidArgumentException('Missing data for URL segment: ' . $segmentName);
+            }
+            throw new InvalidArgumentException(sprintf('Missing RouteData for URL with name: "%s"', $name));
         }
         $url = implode('', $segments);
 
diff --git a/tests/Middleware/ContentLengthMiddlewareTest.php b/tests/Middleware/ContentLengthMiddlewareTest.php
index d2237c644..d31b9c3c8 100644
--- a/tests/Middleware/ContentLengthMiddlewareTest.php
+++ b/tests/Middleware/ContentLengthMiddlewareTest.php
@@ -22,7 +22,7 @@ class ContentLengthMiddlewareTest extends TestCase
 {
     public function testAddsContentLenght()
     {
-        $mw = new ContentLengthMiddleware('append');
+        $mw = new ContentLengthMiddleware();
 
         $uri = Uri::createFromString('https://example.com:443/foo/bar?abc=123');
         $headers = new Headers();
@@ -33,8 +33,9 @@ public function testAddsContentLenght()
         $response = new Response();
 
         $next = function (ServerRequestInterface $req, ResponseInterface $res) {
-            $res->write('Body');
-            return $res;
+            $body = $res->getBody();
+            $body->write('Body');
+            return $res->withBody($body);
         };
 
         $newResponse = $mw($request, $response, $next);
diff --git a/tests/Middleware/OutputBufferingMiddlewareTest.php b/tests/Middleware/OutputBufferingMiddlewareTest.php
index b9b204c82..eedcf1ee5 100644
--- a/tests/Middleware/OutputBufferingMiddlewareTest.php
+++ b/tests/Middleware/OutputBufferingMiddlewareTest.php
@@ -55,10 +55,10 @@ public function testAppend()
         $response = new Response();
 
         $next = function (ServerRequestInterface $req, ResponseInterface $res) {
-            $res->write('Body');
+            $body = $res->getBody();
+            $body->write('Body');
             echo 'Test';
-
-            return $res;
+            return $res->withBody($body);
         };
         $result = $mw($request, $response, $next);
 
@@ -78,10 +78,10 @@ public function testPrepend()
         $response = new Response();
 
         $next = function (ServerRequestInterface $req, ResponseInterface $res) {
-            $res->write('Body');
+            $body = $res->getBody();
+            $body->write('Body');
             echo 'Test';
-
-            return $res;
+            return $res->withBody($body);
         };
         $result = $mw($request, $response, $next);