diff --git a/src/Service/Cache.php b/src/Service/Cache.php
index 35b9ebd..b7fcf37 100644
--- a/src/Service/Cache.php
+++ b/src/Service/Cache.php
@@ -155,7 +155,7 @@ abstract protected function getMandatoryConfig(): array;
      * @param int|float|string|Cacheable $val value to be serialised
      * @return  int|float|string|array value serialized
      */
-    final protected function serializeVal(int|float|string|Cacheable $val): int|float|string|array
+    final protected function serializeVal(int|float|string|Cacheable|null $val): int|float|string|array|null
     {
         if ($val instanceof Cacheable) {
             return ['__cacheable' => 1, '__class' => $val::class, '__data' => $val->serialize()];
diff --git a/tests/AbstractCache.php b/tests/AbstractCache.php
index 66a07bc..27bd4ae 100644
--- a/tests/AbstractCache.php
+++ b/tests/AbstractCache.php
@@ -15,9 +15,7 @@
  */
 abstract class AbstractCache extends TestCase
 {
-
     private ?Cache $cache = null;
-
     private ?Foo $foo = null;
 
     public final function setCache(?Cache $cache): void
@@ -80,7 +78,7 @@ public function testString(): void
 
     public function testArray(): void
     {
-        $x = [1, 2, 3];
+        $x = [1, 2, 3, null];
         $key = 'test_array';
         $res = $this->cache->set($key, $x);
         $this->assertTrue($res);
@@ -149,7 +147,7 @@ public function testClearAllCache(): void
 
     public function testEmptyIncrement(): void
     {
-        $key="test_empty_increment";
+        $key = "test_empty_increment";
         $expected = 1;
         $actual = $this->cache->increment($key);
         $this->assertEquals($expected, $actual);
@@ -157,7 +155,7 @@ public function testEmptyIncrement(): void
 
     public function testEmptyDecrement(): void
     {
-        $key="test_empty_decrement";
+        $key = "test_empty_decrement";
         $expected = -1;
         $actual = $this->cache->decrement($key);
         $this->assertEquals($expected, $actual);
@@ -189,4 +187,4 @@ public final function getCache(): ?Cache
     {
         return $this->cache;
     }
-}
+}
\ No newline at end of file