diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30d362d..a0419e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,17 @@
 # Changelog
 
+## 0.4.0
+
+### Added
+
+- Type hinting for all functions.
+
+### Changed
+
+- PHP 8.0 is now the minimum required version.
+- `phpunit^9.0` is now the minimum required version.
+- Consolidated some redundant functions into one.
+
 ## 0.3.1
 
 ### Fixed
@@ -17,7 +29,6 @@
 - Removed (temporary) paysera/lib-php-cs-fixer-config
 
 ## 0.2.2
-
 ### Fixed
 - Saves originalData and introduces method `getOriginalData` to access it; Adds method `getDataAsArray` to get data in array form
 - remove clone
@@ -25,21 +36,17 @@
 - improve array handling in getObjectWrapperAsArray once more
 
 ## 0.2.1
-
 ### Fixed
 - improve array handling in getObjectWrapperAsArray
 
 ## 0.2.0
-
 ### Added
 - Ability to access originally passed data
 
 ## 0.1.1
-
 ### Fixed
 - Fixed mistype for exception message
 
 ## 0.1.0
-
 ### Fixed
 - Fixes strange test case with PHP 7.0
diff --git a/composer.json b/composer.json
index 926bb00..7a0b1fc 100644
--- a/composer.json
+++ b/composer.json
@@ -7,10 +7,10 @@
         }
     },
     "require": {
-        "php": "^7.0 || ^8.0"
+        "php": ">=8.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.0 || ^9.0"
+        "phpunit/phpunit": "^9.0|^10.0"
     },
     "autoload-dev": {
         "psr-4": {
diff --git a/src/ObjectWrapper.php b/src/ObjectWrapper.php
index 920b611..d4592fc 100644
--- a/src/ObjectWrapper.php
+++ b/src/ObjectWrapper.php
@@ -1,4 +1,5 @@
 <?php
+
 declare(strict_types=1);
 
 namespace Paysera\Component\ObjectWrapper;
@@ -13,11 +14,11 @@
 
 class ObjectWrapper implements ArrayAccess, IteratorAggregate
 {
-    private $data;
-    private $originalData;
-    private $path;
+    private stdClass $data;
+    private stdClass $originalData;
+    private array $path;
 
-    public function __construct(stdClass $data, $path = [])
+    public function __construct(stdClass $data, array $path = [])
     {
         $this->path = $path;
         $this->data = clone $data;
@@ -26,14 +27,14 @@ public function __construct(stdClass $data, $path = [])
         $this->processData();
     }
 
-    private function processData()
+    private function processData(): void
     {
         foreach ($this->data as $key => &$item) {
             $item = $this->processItem($item, [$key]);
         }
     }
 
-    private function processItem($item, array $keys)
+    private function processItem(mixed $item, array $keys): mixed
     {
         if ($item instanceof stdClass) {
             return new self($item, array_merge($this->path, $keys));
@@ -44,7 +45,7 @@ private function processItem($item, array $keys)
         return $item;
     }
 
-    private function processArray(array $data, array $keys)
+    private function processArray(array $data, array $keys): array
     {
         foreach ($data as $i => &$item) {
             $item = $this->processItem($item, array_merge($keys, [(string)$i]));
@@ -53,32 +54,38 @@ private function processArray(array $data, array $keys)
         return $data;
     }
 
-    public function offsetExists($key)
+    public function offsetExists(mixed $offset): bool
     {
-        return isset($this->data->$key);
+        return isset($this->data->$offset);
     }
 
-    public function offsetGet($key)
+    public function offsetGet(mixed $offset): mixed
     {
-        return isset($this->data->$key) ? $this->data->$key : null;
+        return $this->data->$offset ?? null;
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet(mixed $offset, mixed $value): void
     {
         throw new RuntimeException('Modifying ObjectWrapper is not allowed');
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset(mixed $offset): void
     {
         throw new RuntimeException('Modifying ObjectWrapper is not allowed');
     }
 
-    public function getIterator()
+    public function getIterator(): ArrayIterator
     {
         return new ArrayIterator($this->data);
     }
 
-    public function getRequired(string $key)
+    /**
+     * @param string $key
+     *
+     * @return mixed
+     * @throws MissingItemException
+     */
+    public function getRequired(string $key): mixed
     {
         if (!isset($this->data->$key)) {
             throw new MissingItemException($this->buildKey($key));
@@ -92,12 +99,7 @@ public function getRequiredBool(string $key): bool
         return $this->getRequiredOfType($key, 'boolean');
     }
 
-    /**
-     * @param string $key
-     * @param bool|null $default
-     * @return bool|null
-     */
-    public function getBool(string $key, bool $default = null)
+    public function getBool(string $key, ?bool $default = null): ?bool
     {
         return $this->getOfType($key, 'boolean', $default);
     }
@@ -107,12 +109,7 @@ public function getRequiredFloat(string $key): float
         return $this->getRequiredOfType($key, 'float');
     }
 
-    /**
-     * @param string $key
-     * @param float|null $default
-     * @return float|null
-     */
-    public function getFloat(string $key, float $default = null)
+    public function getFloat(string $key, ?float $default = null): ?float
     {
         return $this->getOfType($key, 'float', $default);
     }
@@ -122,26 +119,17 @@ public function getRequiredInt(string $key): int
         return $this->getRequiredOfType($key, 'integer');
     }
 
-    /**
-     * @param string $key
-     * @param int|null $default
-     * @return int|null
-     */
-    public function getInt(string $key, int $default = null)
+    public function getInt(string $key, ?int $default = null): ?int
     {
         return $this->getOfType($key, 'integer', $default);
     }
 
-    public function getRequiredObject(string $key): self
+    public function getRequiredObject(string $key): mixed
     {
         return $this->getRequiredOfType($key, 'object');
     }
 
-    /**
-     * @param string $key
-     * @return ObjectWrapper|null
-     */
-    public function getObject(string $key)
+    public function getObject(string $key): ?ObjectWrapper
     {
         return $this->getOfType($key, 'object', null);
     }
@@ -151,12 +139,7 @@ public function getRequiredString(string $key): string
         return $this->getRequiredOfType($key, 'string');
     }
 
-    /**
-     * @param string $key
-     * @param string|null $default
-     * @return string|null
-     */
-    public function getString(string $key, string $default = null)
+    public function getString(string $key, ?string $default = null): ?string
     {
         return $this->getOfType($key, 'string', $default);
     }
@@ -173,34 +156,15 @@ public function getOriginalData(): stdClass
 
     public function getDataAsArray(): array
     {
-        return $this->getObjectWrapperAsArray($this);
-    }
-
-    private function getObjectWrapperAsArray(ObjectWrapper $objectWrapper)
-    {
-        $data = [];
-        foreach ($objectWrapper as $key => $item) {
-            if ($item instanceof ObjectWrapper) {
-                $data[$key] = $this->getObjectWrapperAsArray($item);
-                continue;
-            } elseif (is_array($item)) {
-                $data[$key] = $this->getObjectWrapperFromArray($item);
-            } else {
-                $data[$key] = $item;
-            }
-        }
-
-        return $data;
+        return $this->recursiveToArray($this);
     }
 
-    private function getObjectWrapperFromArray(array $list)
+    private function recursiveToArray(ArrayAccess|array $inputData): array
     {
         $data = [];
-        foreach ($list as $key => $item) {
-            if ($item instanceof ObjectWrapper) {
-                $data[$key] = $this->getObjectWrapperAsArray($item);
-            } elseif (is_array($item)) {
-                $data[$key] = $this->getObjectWrapperFromArray($item);
+        foreach ($inputData as $key => $item) {
+            if ($item instanceof ArrayAccess || is_array($item)) {
+                $data[$key] = $this->recursiveToArray($item);
             } else {
                 $data[$key] = $item;
             }
@@ -209,14 +173,14 @@ private function getObjectWrapperFromArray(array $list)
         return $data;
     }
 
-    private function getRequiredOfType(string $key, string $expectedType)
+    private function getRequiredOfType(string $key, string $expectedType): mixed
     {
         $value = $this->getRequired($key);
 
         return $this->assertValueType($value, $expectedType, $key);
     }
 
-    private function getOfType(string $key, string $expectedType, $default)
+    private function getOfType(string $key, string $expectedType, $default): mixed
     {
         $value = $this[$key];
         if ($value === null) {
@@ -230,10 +194,11 @@ private function getOfType(string $key, string $expectedType, $default)
      * @param mixed $value
      * @param string $expectedType
      * @param string $key
+     *
      * @return mixed
      * @throws InvalidItemTypeException
      */
-    private function assertValueType($value, string $expectedType, string $key)
+    private function assertValueType(mixed $value, string $expectedType, string $key): mixed
     {
         $givenType = gettype($value);
         if ($givenType === 'double') {
@@ -289,7 +254,7 @@ public function getArrayOfObject(string $key): array
         return $this->getArrayOfType($key, 'object');
     }
 
-    private function getArrayOfType(string $key, string $expectedType)
+    private function getArrayOfType(string $key, string $expectedType): array
     {
         $value = $this->getArray($key);
 
@@ -298,7 +263,7 @@ private function getArrayOfType(string $key, string $expectedType)
         }, $value);
     }
 
-    private function buildKey(string $key)
+    private function buildKey(string $key): string
     {
         return implode('.', array_merge($this->path, [$key]));
     }
diff --git a/tests/ObjectWrapperTest.php b/tests/ObjectWrapperTest.php
index 63c2d52..f5f35dc 100644
--- a/tests/ObjectWrapperTest.php
+++ b/tests/ObjectWrapperTest.php
@@ -1,4 +1,5 @@
 <?php
+
 declare(strict_types=1);
 
 namespace Paysera\Component\ObjectWrapper\Tests;
@@ -12,7 +13,7 @@
 
 class ObjectWrapperTest extends TestCase
 {
-    public function testOffsetExists()
+    public function testOffsetExists(): void
     {
         $object = new ObjectWrapper((object)['a' => 'b', 'c' => ['d' => 'e']]);
         $this->assertTrue(isset($object['a']));
@@ -20,7 +21,7 @@ public function testOffsetExists()
         $this->assertFalse(isset($object['d']));
     }
 
-    public function testOffsetGet()
+    public function testOffsetGet(): void
     {
         $object = new ObjectWrapper((object)['a' => 'b', 'c' => (object)['d' => 'e']]);
         $this->assertSame('b', $object['a']);
@@ -29,27 +30,27 @@ public function testOffsetGet()
         $this->assertInstanceOf(ObjectWrapper::class, $object['c']);
     }
 
-    public function testOffsetSet()
+    public function testOffsetSet(): void
     {
         $this->expectException(RuntimeException::class);
         $object = new ObjectWrapper((object)['a' => 'b', 'c' => ['d' => 'e']]);
         $object['q'] = 'e';
     }
 
-    public function testOffsetUnset()
+    public function testOffsetUnset(): void
     {
         $this->expectException(RuntimeException::class);
         $object = new ObjectWrapper((object)['a' => 'b', 'c' => ['d' => 'e']]);
         unset($object['q']);
     }
 
-    public function testGetIterator()
+    public function testGetIterator(): void
     {
         $object = new ObjectWrapper((object)['a' => 'b', 'c' => ['d' => 'e']]);
         $this->assertSame(['a' => 'b', 'c' => ['d' => 'e']], iterator_to_array($object));
     }
 
-    public function testGetRequired()
+    public function testGetRequired(): void
     {
         $object = new ObjectWrapper((object)['a' => 'b']);
         $this->assertSame('b', $object->getRequired('a'));
@@ -57,42 +58,42 @@ public function testGetRequired()
         $object->getRequired('c');
     }
 
-    public function testGetRequiredBoolWithNoItem()
+    public function testGetRequiredBoolWithNoItem(): void
     {
         $object = new ObjectWrapper((object)[]);
         $this->expectException(MissingItemException::class);
         $object->getRequiredBool('a');
     }
 
-    public function testGetRequiredFloatWithNoItem()
+    public function testGetRequiredFloatWithNoItem(): void
     {
         $object = new ObjectWrapper((object)[]);
         $this->expectException(MissingItemException::class);
         $object->getRequiredFloat('a');
     }
 
-    public function testGetRequiredIntWithNoItem()
+    public function testGetRequiredIntWithNoItem(): void
     {
         $object = new ObjectWrapper((object)[]);
         $this->expectException(MissingItemException::class);
         $object->getRequiredInt('a');
     }
 
-    public function testGetRequiredObjectWithNoItem()
+    public function testGetRequiredObjectWithNoItem(): void
     {
         $object = new ObjectWrapper((object)[]);
         $this->expectException(MissingItemException::class);
         $object->getRequiredObject('a');
     }
 
-    public function testGetRequiredStringWithNoItem()
+    public function testGetRequiredStringWithNoItem(): void
     {
         $object = new ObjectWrapper((object)[]);
         $this->expectException(MissingItemException::class);
         $object->getRequiredString('a');
     }
 
-    public function testGetRequiredBool()
+    public function testGetRequiredBool(): void
     {
         $object = new ObjectWrapper((object)['a' => true, 'b' => 'other type', 'c' => 'false', 'd' => '1', 'e' => 0]);
         $this->assertTrue($object->getRequiredBool('a'));
@@ -103,16 +104,16 @@ public function testGetRequiredBool()
         $object->getRequiredBool('b');
     }
 
-    public function testGetRequiredFloat()
+    public function testGetRequiredFloat(): void
     {
         $object = new ObjectWrapper((object)['a' => 1.23, 'b' => 1, 'c' => 'other type']);
         $this->assertSame(1.23, $object->getRequiredFloat('a'));
-        $this->assertSame((float)1, $object->getRequiredFloat('b'));
+        $this->assertSame(1.0, $object->getRequiredFloat('b'));
         $this->expectException(InvalidItemTypeException::class);
         $object->getRequiredFloat('c');
     }
 
-    public function testGetRequiredInt()
+    public function testGetRequiredInt(): void
     {
         $object = new ObjectWrapper((object)['a' => 1, 'b' => 1.23]);
         $this->assertSame(1, $object->getRequiredInt('a'));
@@ -120,7 +121,7 @@ public function testGetRequiredInt()
         $object->getRequiredInt('b');
     }
 
-    public function testGetRequiredObject()
+    public function testGetRequiredObject(): void
     {
         $data = new stdClass();
         $data->a = 'a';
@@ -130,7 +131,7 @@ public function testGetRequiredObject()
         $object->getRequiredObject('b');
     }
 
-    public function testGetRequiredString()
+    public function testGetRequiredString(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string', 'b' => 123]);
         $this->assertSame('string', $object->getRequiredString('a'));
@@ -138,7 +139,7 @@ public function testGetRequiredString()
         $object->getRequiredString('b');
     }
 
-    public function testGetBool()
+    public function testGetBool(): void
     {
         $object = new ObjectWrapper((object)['a' => true, 'b' => 'other type']);
         $this->assertTrue($object->getBool('a'));
@@ -148,7 +149,7 @@ public function testGetBool()
         $object->getRequiredBool('b');
     }
 
-    public function testGetFloat()
+    public function testGetFloat(): void
     {
         $object = new ObjectWrapper((object)['a' => 1.23, 'b' => 1, 'c' => 'other type']);
         $this->assertSame(1.23, $object->getFloat('a'));
@@ -159,7 +160,7 @@ public function testGetFloat()
         $object->getFloat('c');
     }
 
-    public function testGetInt()
+    public function testGetInt(): void
     {
         $object = new ObjectWrapper((object)['a' => 1, 'b' => 1.23]);
         $this->assertSame(1, $object->getInt('a'));
@@ -169,7 +170,7 @@ public function testGetInt()
         $object->getInt('b');
     }
 
-    public function testGetObject()
+    public function testGetObject(): void
     {
         $data = new stdClass();
         $data->a = 'a';
@@ -180,7 +181,7 @@ public function testGetObject()
         $object->getObject('b');
     }
 
-    public function testGetString()
+    public function testGetString(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string', 'b' => 123]);
         $this->assertSame('string', $object->getString('a'));
@@ -190,7 +191,7 @@ public function testGetString()
         $object->getString('b');
     }
 
-    public function testGetArray()
+    public function testGetArray(): void
     {
         $array = [1, '2', 3.0, false, (object)['a' => 'b']];
         $object = new ObjectWrapper((object)['a' => $array, 'empty' => []]);
@@ -200,20 +201,20 @@ public function testGetArray()
         $this->assertSame([], $object->getArray('empty', [1, 2, 3]));
     }
 
-    public function testGetArrayWithDifferentType()
+    public function testGetArrayWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string']);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArray('a');
     }
 
-    public function testGetArrayWithNull()
+    public function testGetArrayWithNull(): void
     {
         $object = new ObjectWrapper((object)['a' => null]);
         $this->assertSame([], $object->getArray('a'));
     }
 
-    public function testGetArrayOfBool()
+    public function testGetArrayOfBool(): void
     {
         $array = [false, false, true];
         $object = new ObjectWrapper((object)['a' => $array, 'empty' => []]);
@@ -222,14 +223,14 @@ public function testGetArrayOfBool()
         $this->assertSame([], $object->getArrayOfBool('empty'));
     }
 
-    public function testGetArrayOfBoolWithDifferentType()
+    public function testGetArrayOfBoolWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string']);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfBool('a');
     }
 
-    public function testGetArrayOfBoolWithDifferentItemType()
+    public function testGetArrayOfBoolWithDifferentItemType(): void
     {
         $array = [false, 'false', 0, true, 1, 'true'];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -239,7 +240,7 @@ public function testGetArrayOfBoolWithDifferentItemType()
         );
     }
 
-    public function testGetArrayOfFloat()
+    public function testGetArrayOfFloat(): void
     {
         $array = [1, 1.0, 2.3];
         $object = new ObjectWrapper((object)['a' => $array, 'empty' => []]);
@@ -248,14 +249,14 @@ public function testGetArrayOfFloat()
         $this->assertSame([], $object->getArrayOfFloat('empty'));
     }
 
-    public function testGetArrayOfFloatWithDifferentType()
+    public function testGetArrayOfFloatWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string']);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfFloat('a');
     }
 
-    public function testGetArrayOfFloatWithDifferentItemType()
+    public function testGetArrayOfFloatWithDifferentItemType(): void
     {
         $array = [1.0, 2.3, false];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -263,7 +264,7 @@ public function testGetArrayOfFloatWithDifferentItemType()
         $object->getArrayOfFloat('a');
     }
 
-    public function testGetArrayOfFloatWithNullItem()
+    public function testGetArrayOfFloatWithNullItem(): void
     {
         $array = [1.0, 2.0, null, 3.3];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -271,7 +272,7 @@ public function testGetArrayOfFloatWithNullItem()
         $object->getArrayOfFloat('a');
     }
 
-    public function testGetArrayOfInt()
+    public function testGetArrayOfInt(): void
     {
         $array = [0, -10, 2211223];
         $object = new ObjectWrapper((object)['a' => $array, 'empty' => []]);
@@ -280,14 +281,14 @@ public function testGetArrayOfInt()
         $this->assertSame([], $object->getArrayOfInt('empty'));
     }
 
-    public function testGetArrayOfIntWithDifferentType()
+    public function testGetArrayOfIntWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string']);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfInt('a');
     }
 
-    public function testGetArrayOfIntWithDifferentItemType()
+    public function testGetArrayOfIntWithDifferentItemType(): void
     {
         $array = [1, 9, 2.1, 4];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -295,7 +296,7 @@ public function testGetArrayOfIntWithDifferentItemType()
         $object->getArrayOfInt('a');
     }
 
-    public function testGetArrayOfIntWithNullItem()
+    public function testGetArrayOfIntWithNullItem(): void
     {
         $array = [1, 3, null, 5];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -303,7 +304,7 @@ public function testGetArrayOfIntWithNullItem()
         $object->getArrayOfInt('a');
     }
 
-    public function testGetArrayOfString()
+    public function testGetArrayOfString(): void
     {
         $array = ['', '123123', 'string'];
         $object = new ObjectWrapper((object)['a' => $array, 'empty' => []]);
@@ -312,14 +313,14 @@ public function testGetArrayOfString()
         $this->assertSame([], $object->getArrayOfString('empty'));
     }
 
-    public function testGetArrayOfStringWithDifferentType()
+    public function testGetArrayOfStringWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 1]);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfString('a');
     }
 
-    public function testGetArrayOfStringWithDifferentItemType()
+    public function testGetArrayOfStringWithDifferentItemType(): void
     {
         $array = ['string', 'aaa', 4];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -327,7 +328,7 @@ public function testGetArrayOfStringWithDifferentItemType()
         $object->getArrayOfString('a');
     }
 
-    public function testGetArrayOfStringWithNullItem()
+    public function testGetArrayOfStringWithNullItem(): void
     {
         $array = ['string', 'item', null];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -335,7 +336,7 @@ public function testGetArrayOfStringWithNullItem()
         $object->getArrayOfString('a');
     }
 
-    public function testGetArrayOfObject()
+    public function testGetArrayOfObject(): void
     {
         $structure = new stdClass();
         $jsonStructure = json_decode('{"a":"b"}');
@@ -346,21 +347,21 @@ public function testGetArrayOfObject()
         $this->assertSame([], $object->getArrayOfObject('empty'));
     }
 
-    public function testGetArrayOfObjectWithDifferentType()
+    public function testGetArrayOfObjectWithDifferentType(): void
     {
         $object = new ObjectWrapper((object)['a' => 1]);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfObject('a');
     }
 
-    public function testGetArrayOfObjectWithDifferentItemType()
+    public function testGetArrayOfObjectWithDifferentItemType(): void
     {
         $object = new ObjectWrapper((object)['a' => 'string']);
         $this->expectException(InvalidItemTypeException::class);
         $object->getArrayOfObject('a');
     }
 
-    public function testGetArrayOfObjectWithNullItem()
+    public function testGetArrayOfObjectWithNullItem(): void
     {
         $array = [(object)['a' => 'b'], (object)[0 => 0, 1 => 1], null];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -368,7 +369,7 @@ public function testGetArrayOfObjectWithNullItem()
         $object->getArrayOfObject('a');
     }
 
-    public function testGetArrayOfObjectWithAssociativeArrayItem()
+    public function testGetArrayOfObjectWithAssociativeArrayItem(): void
     {
         $array = [(object)['a' => 'b'], (object)[0 => 0, 1 => 1], ['a' => 'b']];
         $object = new ObjectWrapper((object)['a' => $array]);
@@ -376,7 +377,7 @@ public function testGetArrayOfObjectWithAssociativeArrayItem()
         $object->getArrayOfObject('a');
     }
 
-    public function testDoesNotAffectInput()
+    public function testDoesNotAffectInput(): void
     {
         $innerData = (object)['b' => 'c'];
         $data = new stdClass();
@@ -386,7 +387,7 @@ public function testDoesNotAffectInput()
         $this->assertSame($innerData, $data->a);
     }
 
-    public function testGetOriginalData()
+    public function testGetOriginalData(): void
     {
         $innerData = (object)['b' => 'c'];
         $data = new stdClass();
@@ -396,7 +397,7 @@ public function testGetOriginalData()
         $this->assertDeepEquals($data, $originalData);
     }
 
-    public function testGetOriginalDataAsArray()
+    public function testGetOriginalDataAsArray(): void
     {
         $innerData = (object)['b' => 'c'];
         $data = new stdClass();
@@ -425,12 +426,12 @@ public function testGetOriginalDataAsArray()
         $this->assertDeepEquals($expectedArray, $originalData);
     }
 
-    private function assertDeepEquals($expectedData, $dataWithWrappers)
+    private function assertDeepEquals($expectedData, $dataWithWrappers): void
     {
         $this->assertEquals($expectedData, $this->unwrap($dataWithWrappers));
     }
 
-    private function unwrap($dataWithWrappers)
+    private function unwrap($dataWithWrappers): mixed
     {
         if ($dataWithWrappers instanceof ObjectWrapper) {
             $result = new stdClass();