diff --git a/.travis.yml b/.travis.yml
index a45cf8011..5b46a2a76 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,7 +8,7 @@ import:
 jobs:
   fast_finish: true
   include:
-    - php: 7.3
+    - php: 7.4
       env:
         - DB=MYSQL
         - REQUIRE_INSTALLER="$REQUIRE_RECIPE"
@@ -28,15 +28,17 @@ jobs:
         - REQUIRE_INSTALLER="$REQUIRE_RECIPE"
         - PHPUNIT_TEST=1
         - PHPUNIT_SUITE="cms"
-    - php: 7.4
-      env:
-        - DB=MYSQL
-        - REQUIRE_INSTALLER="$REQUIRE_RECIPE"
-        - PHPUNIT_TEST=1
-        - PHPUNIT_SUITE="framework"
     - php: 8.0
       env:
         - DB=MYSQL
         - REQUIRE_INSTALLER="$REQUIRE_RECIPE"
         - PHPUNIT_TEST=1
         - PHPUNIT_SUITE="framework"
+    - php: 8.1.0
+      env:
+        - DB=MYSQL
+        - REQUIRE_INSTALLER="$REQUIRE_RECIPE"
+        - PHPUNIT_TEST=1
+        - PHPUNIT_SUITE="framework"
+  allow_failures:
+    - php: 8.1.0
diff --git a/composer.json b/composer.json
index 465c5b6e8..573b7bcb8 100644
--- a/composer.json
+++ b/composer.json
@@ -40,7 +40,7 @@
         "symfony/config": "^3.4 || ^4.0",
         "symfony/translation": "^3.4 || ^4.0",
         "symfony/yaml": "^3.4 || ^4.0",
-        "php": "^7.3 || ^8.0",
+        "php": "^7.4 || ^8.0",
         "ext-ctype": "*",
         "ext-dom": "*",
         "ext-hash": "*",
@@ -58,6 +58,7 @@
         "squizlabs/php_codesniffer": "^3.5"
     },
     "conflict": {
+        "egulias/email-validator": "^2",
         "phpunit/phpunit": "^6 || ^7 || ^8"
     },
     "provide": {
diff --git a/src/Core/Manifest/Module.php b/src/Core/Manifest/Module.php
index 23a974fb3..8a408fa13 100644
--- a/src/Core/Manifest/Module.php
+++ b/src/Core/Manifest/Module.php
@@ -185,11 +185,42 @@ class Module implements Serializable
         return substr($this->path, strlen($this->basePath) + 1);
     }
 
+    public function __serialize(): array
+    {
+        return [
+            'path' => $this->path,
+            'basePath' => $this->basePath,
+            'composerData' => $this->composerData
+        ];
+    }
+
+    public function __unserialize(array $data): void
+    {
+            $this->path = $data['path'];
+            $this->basePath = $data['basePath'];
+            $this->composerData = $data['composerData'];
+            $this->resources = [];
+    }
+
+    /**
+     * The __serialize() magic method will be automatically used instead of this
+     *
+     * @return string
+     * @deprecated will be removed in 5.0
+     */
     public function serialize()
     {
         return json_encode([$this->path, $this->basePath, $this->composerData]);
     }
 
+    /**
+     * The __unserialize() magic method will be automatically used instead of this almost all the time
+     * This method will be automatically used if existing serialized data was not saved as an associative array
+     * and the PHP version used in less than PHP 9.0
+     *
+     * @param string $serialized
+     * @deprecated will be removed in 5.0
+     */
     public function unserialize($serialized)
     {
         list($this->path, $this->basePath, $this->composerData) = json_decode($serialized, true);
diff --git a/src/ORM/ValidationResult.php b/src/ORM/ValidationResult.php
index e839387d1..5f852131d 100644
--- a/src/ORM/ValidationResult.php
+++ b/src/ORM/ValidationResult.php
@@ -214,10 +214,25 @@ class ValidationResult implements Serializable
         return $this;
     }
 
+    public function __serialize(): array
+    {
+        return [
+            'messages' => $this->messages,
+            'isValid' => $this->isValid()
+        ];
+    }
+
+    public function __unserialize(array $data): void
+    {
+        $this->messages = $data['messages'];
+        $this->isValid = $data['isValid'];
+    }
+
     /**
-     * String representation of object
+     * The __serialize() magic method will be automatically used instead of this
      *
-     * @return string the string representation of the object or null
+     * @return string
+     * @deprecated will be removed in 5.0
      */
     public function serialize()
     {
@@ -225,9 +240,12 @@ class ValidationResult implements Serializable
     }
 
     /**
-     * Constructs the object
+     * The __unserialize() magic method will be automatically used instead of this almost all the time
+     * This method will be automatically used if existing serialized data was not saved as an associative array
+     * and the PHP version used in less than PHP 9.0
      *
      * @param string $serialized
+     * @deprecated will be removed in 5.0
      */
     public function unserialize($serialized)
     {
diff --git a/src/i18n/Messages/Symfony/FlushInvalidatedResource.php b/src/i18n/Messages/Symfony/FlushInvalidatedResource.php
index 0e01f45f1..72b4487a1 100644
--- a/src/i18n/Messages/Symfony/FlushInvalidatedResource.php
+++ b/src/i18n/Messages/Symfony/FlushInvalidatedResource.php
@@ -40,11 +40,35 @@ class FlushInvalidatedResource implements SelfCheckingResourceInterface, \Serial
         return false;
     }
 
+    public function __serialize(): array
+    {
+        return [];
+    }
+
+    public function __unserialize(array $data): void
+    {
+        // no-op
+    }
+
+    /**
+     * The __serialize() magic method will be automatically used instead of this
+     *
+     * @return string
+     * @deprecated will be removed in 5.0
+     */
     public function serialize()
     {
         return '';
     }
 
+    /**
+     * The __unserialize() magic method will be automatically used instead of this almost all the time
+     * This method will be automatically used if existing serialized data was not saved as an associative array
+     * and the PHP version used in less than PHP 9.0
+     *
+     * @param string $serialized
+     * @deprecated will be removed in 5.0
+     */
     public function unserialize($serialized)
     {
         // no-op