Fix issues detected by Psalm

src/Dispatching/DispatchStack.php

@@ -26,7 +26,7 @@ class DispatchStack implements DispatchStackInterface
      * Push a new middleware onto the stack.
      *
      * @param mixed $middleware Middleware to dispatch in sequence
-     * @return self
+     * @return static
      */
     public function add($middleware)
     {

src/Message/Message.php

@@ -101,7 +101,7 @@ abstract class Message implements MessageInterface
      * While header names are not case-sensitive, getHeaders() will preserve the
      * exact case in which headers were originally specified.
      *
-     * @return array Returns an associative array of the message's headers.
+     * @return string[][] Returns an associative array of the message's headers.
      */
     public function getHeaders()
     {

src/Message/NullStream.php

@@ -51,9 +51,10 @@ class NullStream implements StreamInterface
     }
 
     /**
-     * Returns 0
+     * Returns the current position of the file read/write pointer
      *
-     * @return int|bool Position of the file pointer or false on error.
+     * @return int Position of the file pointer
+     * @throws \RuntimeException on error.
      */
     public function tell()
     {

src/Message/Request.php

@@ -212,7 +212,7 @@ class Request extends Message implements RequestInterface
 
     /**
      * @param string $method
-     * @return static
+     * @return string
      * @throws \InvalidArgumentException
      */
     private function getValidatedMethod($method)

src/Message/Stream.php

@@ -67,7 +67,9 @@ class Stream implements StreamInterface
      */
     public function close()
     {
-        fclose($this->resource);
+        $resource = $this->resource;
+        fclose($resource);
+        $this->resource = null;
     }
 
     /**
@@ -79,9 +81,9 @@ class Stream implements StreamInterface
      */
     public function detach()
     {
-        $stream = $this->resource;
+        $resource = $this->resource;
         $this->resource = null;
-        return $stream;
+        return $resource;
     }
 
     /**

src/Routing/Router.php

@@ -203,7 +203,7 @@ class Router
     }
 
     /**
-     * @param DispatcherInterface
+     * @param DispatcherInterface $dispatcher
      * @return RouteFactoryInterface
      */
     protected function getRouteFactory($dispatcher)
@@ -266,21 +266,21 @@ class Router
             }
         );
 
-        if ($matches) {
+        if (!$matches) {
-            if (count($matches) > 0) {
+            return null;
-                // If there are multiple matches, sort them to find the one with
+        }
-                // the longest string length.
+
+        // If there are multiple matches, sort them to find the one with the
+        // longest string length.
+        if (count($matches) > 1) {
             $compareByLength = function ($a, $b) {
                 return strlen($b) - strlen($a);
             };
             usort($matches, $compareByLength);
         }
-            /** @var string $bestMatch */
+
         $bestMatch = $matches[0];
-            $route = $this->prefixRoutes[$bestMatch];
+        return $this->prefixRoutes[$bestMatch];
-            return $route;
-        }
-        return null;
     }
 
     private function startsWith($haystack, $needle)