PHP 8.4 - implicit nulls are deprecated

`MobileDetect::__construct(): Implicitly marking parameter $cache as nullable is deprecated, the explicit nullable type must be used instead`
`CacheException::__construct(): Implicitly marking parameter $previous as nullable is deprecated, the explicit nullable type must be used instead`

Updated Github Actions workflow to include PHP 8.4

Fixes #956
Replaces #957

.github/workflows/4.8.x-test.yml

@@ -24,12 +24,10 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        php-version: [8.0, 8.1, 8.2, 8.3]
+        php-version: [8.0, 8.1, 8.2, 8.3, 8.4]
         os: ['ubuntu-latest']
-        include:
-          - os: 'ubuntu-latest'
-            phpunit-version: '9.6.10'
-            composer-version: 'latest'
+        composer-version: ['latest']
+        phpunit-version: ['^9.6.18']
     steps:
       - name: Checkout
         uses: actions/checkout@v3

composer.json

@@ -19,7 +19,7 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^v3.35.1",
-        "phpunit/phpunit": "^9.6",
+        "phpunit/phpunit": "^9.6.18",
         "squizlabs/php_codesniffer": "^3.7",
         "phpbench/phpbench": "^1.2",
         "phpstan/phpstan": "^1.10"

src/Cache/CacheException.php

@@ -6,7 +6,7 @@
 
 class CacheException extends \Exception
 {
-    public function __construct($message, $code = 0, \Throwable $previous = null)
+    public function __construct($message, $code = 0, ?\Throwable $previous = null)
     {
         // some code
 

src/MobileDetect.php

@@ -1028,11 +1028,11 @@ class MobileDetect
      * Construct an instance of this class.
      */
     public function __construct(
-        Cache $cache = null,
+        ?Cache $cache = null,
         array $config = [],
     ) {
         // If no custom cache provided then use our own.
-        $this->cache = $cache == null ? new Cache() : $cache;
+        $this->cache = $cache ?? new Cache();
         // Override config from user.
         $this->config = array_merge($this->config, $config);