diff --git a/src/Entities/Subscription.php b/src/Entities/Subscription.php
index 41d242c..c44f895 100644
--- a/src/Entities/Subscription.php
+++ b/src/Entities/Subscription.php
@@ -21,7 +21,7 @@ use D3\KlicktippPhpClient\Exceptions\BaseException;
 use D3\KlicktippPhpClient\Resources\SubscriptionProcess;
 use Doctrine\Common\Collections\ArrayCollection;
 
-class Subscription extends ArrayCollection
+class Subscription extends Entity
 {
     private ?SubscriptionProcess $endpoint;
 
@@ -31,14 +31,14 @@ class Subscription extends ArrayCollection
         parent::__construct($elements);
     }
 
-    public function getListId(): string
+    public function getListId(): ?string
     {
-        return $this->get(SubscriptionProcess::LISTID) ?? '';
+        return $this->getStringOrNullValue($this->get(SubscriptionProcess::LISTID));
     }
 
-    public function getName(): string
+    public function getName(): ?string
     {
-        return $this->get(SubscriptionProcess::NAME) ?? '';
+        return $this->getStringOrNullValue($this->get(SubscriptionProcess::NAME));
     }
 
     public function setName(string $name): void
@@ -46,34 +46,34 @@ class Subscription extends ArrayCollection
         $this->set(SubscriptionProcess::NAME, $name);
     }
 
-    public function getPendingUrl(): string
+    public function getPendingUrl(): ?string
     {
-        return $this->get(SubscriptionProcess::PENDINGURL) ?? '';
+        return $this->getStringOrNullValue($this->get(SubscriptionProcess::PENDINGURL));
     }
 
-    public function getThankyouUrl(): string
+    public function getThankyouUrl(): ?string
     {
-        return $this->get(SubscriptionProcess::THANKYOUURL) ?? '';
+        return $this->getStringOrNullValue($this->get(SubscriptionProcess::THANKYOUURL));
     }
 
-    public function useSingleOptin(): bool
+    public function useSingleOptin(): ?bool
     {
-        return $this->get(SubscriptionProcess::USE_SINGLE_OPTIN);
+        return $this->getBooleanOrNullValue($this->get(SubscriptionProcess::USE_SINGLE_OPTIN));
     }
 
-    public function useDoubleOptin(): bool
+    public function useDoubleOptin(): ?bool
     {
-        return !$this->useSingleOptin();
+        return is_null($soi = $this->useSingleOptin()) ? null : !$soi;
     }
 
-    public function resendConfirmationEmail(): bool
+    public function resendConfirmationEmail(): ?bool
     {
-        return $this->get(SubscriptionProcess::RESEND_CONFIRMATION_EMAIL);
+        return $this->getBooleanOrNullValue($this->get(SubscriptionProcess::RESEND_CONFIRMATION_EMAIL));
     }
 
-    public function useChangeEmail(): bool
+    public function useChangeEmail(): ?bool
     {
-        return $this->get(SubscriptionProcess::USE_CHANGE_EMAIL);
+        return $this->getBooleanOrNullValue($this->get(SubscriptionProcess::USE_CHANGE_EMAIL));
     }
 
     /**
diff --git a/tests/unit/Entities/SubscriptionTest.php b/tests/unit/Entities/SubscriptionTest.php
new file mode 100644
index 0000000..5bfd2d1
--- /dev/null
+++ b/tests/unit/Entities/SubscriptionTest.php
@@ -0,0 +1,238 @@
+<?php
+
+/**
+ * Copyright (c) D3 Data Development (Inh. Thomas Dartsch)
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ *
+ * https://www.d3data.de
+ *
+ * @copyright (C) D3 Data Development (Inh. Thomas Dartsch)
+ * @author    D3 Data Development - Daniel Seifert <info@shopmodule.com>
+ * @link      https://www.oxidmodule.com
+ */
+
+declare(strict_types=1);
+
+namespace D3\KlicktippPhpClient\tests\unit\Entities;
+
+use D3\KlicktippPhpClient\Entities\Subscription;
+use D3\KlicktippPhpClient\Exceptions\InvalidCredentialTypeException;
+use D3\KlicktippPhpClient\Resources\SubscriptionProcess as SubscriptionEndpoint;
+use D3\KlicktippPhpClient\tests\TestCase;
+use Generator;
+use PHPUnit\Framework\MockObject\Rule\InvokedCount;
+use ReflectionException;
+
+/**
+ * @covers \D3\KlicktippPhpClient\Entities\Subscriber
+ */
+class SubscriptionTest extends TestCase
+{
+    public function setUp(): void
+    {
+        parent::setUp();
+        $this->entity = new Subscription(
+            [
+                SubscriptionEndpoint::LISTID                    => "368370",
+                SubscriptionEndpoint::NAME                      => "subscriptionName",
+                SubscriptionEndpoint::PENDINGURL                => "pendingFixture",
+                SubscriptionEndpoint::THANKYOUURL               => "thankyouFixture",
+                SubscriptionEndpoint::USE_SINGLE_OPTIN          => true,
+                SubscriptionEndpoint::RESEND_CONFIRMATION_EMAIL => false,
+                SubscriptionEndpoint::USE_CHANGE_EMAIL          => false,
+
+            ]
+        );
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::__construct
+     */
+    public function testConstruct(): void
+    {
+        $elements = [
+            'key1' => 'value1',
+            'key2' => 'value2',
+        ];
+
+        $endpoint = $this->getMockBuilder(SubscriptionEndpoint::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $sut = new Subscription($elements, $endpoint);
+
+        $this->assertSame(
+            $elements,
+            $sut->toArray()
+        );
+        $this->assertSame(
+            $endpoint,
+            $this->getValue($sut, 'endpoint')
+        );
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getListId
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getName
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getPendingUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getThankyouUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useSingleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useDoubleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::resendConfirmationEmail
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useChangeEmail
+     * @dataProvider getDataProvider
+     */
+    public function testGet(string $methodName, bool|string $expectedValue): void
+    {
+        $this->assertSame(
+            $expectedValue,
+            $this->callMethod($this->entity, $methodName)
+        );
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getListId
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getName
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getPendingUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getThankyouUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useSingleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useDoubleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::resendConfirmationEmail
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useChangeEmail
+     * @dataProvider getDataProvider
+     */
+    public function testGetNull(string $testMethod): void
+    {
+        $nullProperties = [];
+        foreach (array_keys($this->entity->toArray()) as $key) {
+            $nullProperties[$key] = null;
+        }
+
+        $sut = new Subscription($nullProperties);
+
+        $this->assertNull(
+            $this->callMethod(
+                $sut,
+                $testMethod,
+            )
+        );
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getListId
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getName
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getPendingUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::getThankyouUrl
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useSingleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useDoubleOptin
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::resendConfirmationEmail
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::useChangeEmail
+     * @dataProvider getDataProvider
+     */
+    public function testGetInvalid(string $testMethod): void
+    {
+        $invalidProperties = [
+            SubscriptionEndpoint::LISTID            => [],
+            SubscriptionEndpoint::NAME              => [],
+            SubscriptionEndpoint::PENDINGURL        => false,
+            SubscriptionEndpoint::THANKYOUURL       => [],
+            SubscriptionEndpoint::USE_SINGLE_OPTIN  => "string",
+            SubscriptionEndpoint::RESEND_CONFIRMATION_EMAIL => [],
+            SubscriptionEndpoint::USE_CHANGE_EMAIL  => 'string',
+        ];
+
+        $sut = new Subscription($invalidProperties);
+
+        $this->expectException(InvalidCredentialTypeException::class);
+
+        $this->assertNull(
+            $this->callMethod(
+                $sut,
+                $testMethod,
+            )
+        );
+    }
+
+    public static function getDataProvider(): Generator
+    {
+        yield ['getListId', '368370'];
+        yield ['getName', 'subscriptionName'];
+        yield ['getPendingUrl', 'pendingFixture'];
+        yield ['getThankyouUrl', 'thankyouFixture'];
+        yield ['useSingleOptin', true];
+        yield ['useDoubleOptin', false];
+        yield ['resendConfirmationEmail', false];
+        yield ['useChangeEmail', false];
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::setName
+     */
+    public function testSetname(): void {
+        $sut = $this->getMockBuilder(Subscription::class)
+            ->onlyMethods(['set'])
+            ->setConstructorArgs([[SubscriptionEndpoint::LISTID => 'foo']])
+            ->getMock();
+        $sut->expects($this->once())->method('set')->with(
+            $this->identicalTo(SubscriptionEndpoint::NAME)
+        );
+
+        $this->callMethod(
+            $sut,
+            "setName",
+            ['newValue']
+        );
+    }
+
+    /**
+     * @test
+     * @throws ReflectionException
+     * @covers \D3\KlicktippPhpClient\Entities\Subscription::persist
+     * @dataProvider persistDataProvider
+     */
+    public function testPersist(
+        bool $endpointSet,
+        InvokedCount $endpointInvocation,
+        ?bool $expectedReturn
+    ): void {
+        $endpointMock = $this->getMockBuilder(SubscriptionEndpoint::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['update'])
+            ->getMock();
+        $endpointMock->expects($endpointInvocation)->method('update')->with(
+            $this->identicalTo('foo'),
+            $this->identicalTo('bar'),
+        )->willReturn(true);
+
+        $sut = new Subscription(
+            [SubscriptionEndpoint::LISTID => 'foo', SubscriptionEndpoint::NAME  => 'bar'],
+            $endpointSet ? $endpointMock : null
+        );
+
+        $this->assertSame(
+            $expectedReturn,
+            $this->callMethod(
+                $sut,
+                'persist'
+            )
+        );
+    }
+
+    public static function persistDataProvider(): Generator
+    {
+        yield 'has endpoint'    => [true, self::once(), true];
+        yield 'has no endpoint'    => [false, self::never(), null];
+    }
+}