diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 30eeaeb..9624993 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,22 +7,26 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php_version: [7.3, 7.4, 8.0]
+        php_version: [7.4, 8.0, 8.1]
         composer_flags: ['', '--prefer-lowest']
 
     steps:
     - uses: actions/checkout@v2
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php_version }}
+        extensions: xdebug
+
     - uses: php-actions/composer@v5
       with:
         php_version: ${{ matrix.php_version }}
         args: ${{ matrix.composer_flags }}
         command: update
-    - uses: php-actions/phpunit@v3
-      with:
-        version: 8
-        php_version: ${{ matrix.php_version }}
-        args: '--coverage-clover ./tests/logs/clover.xml'
-        php_extensions: xdebug
+
+    - name: Run tests
+      run: ./vendor/bin/phpunit --coverage-clover ./tests/logs/clover.xml
       env:
           XDEBUG_MODE: coverage
 
diff --git a/composer.json b/composer.json
index 90c7a09..058ee55 100755
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
     },
     "require-dev": {
         "php-di/php-di": "^6.3.4",
-        "phpunit/phpunit": "^8.0",
+        "phpunit/phpunit": "^9.5",
         "php-coveralls/php-coveralls": "^2.4",
         "mockery/mockery": "^1.4.3",
         "squizlabs/php_codesniffer": "^3.6.0"
diff --git a/src/RouteGroup.php b/src/RouteGroup.php
index 4b192f2..54f3db5 100644
--- a/src/RouteGroup.php
+++ b/src/RouteGroup.php
@@ -34,7 +34,7 @@ public function __construct($params, $router)
             $this->middleware += $middleware;
         }
 
-        $this->prefix = trim($prefix, ' /');
+        $this->prefix = is_string($prefix) ? trim($prefix, ' /') : null;
         $this->router = $router;
     }
 
@@ -43,12 +43,12 @@ private function appendPrefixToUri(string $uri)
         return $this->prefix . '/' . ltrim($uri, '/');
     }
 
-    public function map(array $verbs, string $uri, $callback) : Route
+    public function map(array $verbs, string $uri, $callback): Route
     {
         return $this->router->map($verbs, $this->appendPrefixToUri($uri), $callback)->middleware($this->middleware);
     }
 
-    public function group($params, $callback) : RouteGroup
+    public function group($params, $callback): RouteGroup
     {
         if (is_string($params)) {
             $params = $this->appendPrefixToUri($params);
diff --git a/src/RouteParams.php b/src/RouteParams.php
index 3a72cce..7c972bb 100644
--- a/src/RouteParams.php
+++ b/src/RouteParams.php
@@ -21,27 +21,32 @@ public function __get($key)
         return $this->params[$key];
     }
 
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->position = 0;
     }
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->params[$this->key()];
     }
 
+    #[\ReturnTypeWillChange]
     public function key()
     {
         $keys = array_keys($this->params);
         return $keys[$this->position];
     }
 
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->position++;
     }
 
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return $this->position < count($this->params);
diff --git a/src/Router.php b/src/Router.php
index 8595a9c..11d8374 100644
--- a/src/Router.php
+++ b/src/Router.php
@@ -239,11 +239,11 @@ public function url(string $name, $params = [])
         try {
             return $this->altoRouter->generate($name, $params);
         } catch (\Exception $e) {
-            throw new NamedRouteNotFoundException($name, null);
+            throw new NamedRouteNotFoundException($name);
         }
     }
 
-    public function group($params, $callback) : Router
+    public function group($params, $callback): Router
     {
         $group = new RouteGroup($params, $this);