diff --git a/Classes/DataProcessing/ContainerProcessor.php b/Classes/DataProcessing/ContainerProcessor.php
index 4c58f986..8fc0fc26 100644
--- a/Classes/DataProcessing/ContainerProcessor.php
+++ b/Classes/DataProcessing/ContainerProcessor.php
@@ -51,7 +51,7 @@ public function process(
         }
         $contentId = null;
         if ($processorConfiguration['contentId.'] ?? false) {
-            $contentId = (int)$cObj->stdWrap($processorConfiguration['contentId'], $processorConfiguration['contentId.']);
+            $contentId = (int)$cObj->stdWrap($processorConfiguration['contentId'] ?? '', $processorConfiguration['contentId.']);
         } elseif ($processorConfiguration['contentId'] ?? false) {
             $contentId = (int)$processorConfiguration['contentId'];
         }
diff --git a/Tests/Unit/DataProcessing/ContainerProcessorTest.php b/Tests/Unit/DataProcessing/ContainerProcessorTest.php
new file mode 100644
index 00000000..abcae657
--- /dev/null
+++ b/Tests/Unit/DataProcessing/ContainerProcessorTest.php
@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace B13\Container\Tests\Unit\DataProcessing;
+
+/*
+ * This file is part of TYPO3 CMS-based extension "container" by b13.
+ *
+ * It is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License, either version 2
+ * of the License, or any later version.
+ */
+
+use B13\Container\DataProcessing\ContainerProcessor;
+use B13\Container\Domain\Factory\FrontendContainerFactory;
+use B13\Container\Domain\Model\Container;
+use TYPO3\CMS\Core\Context\Context;
+use TYPO3\CMS\Frontend\ContentObject\ContentDataProcessor;
+use TYPO3\CMS\Frontend\ContentObject\ContentObjectRenderer;
+use TYPO3\TestingFramework\Core\Unit\UnitTestCase;
+
+class ContainerProcessorTest extends UnitTestCase
+{
+    protected bool $resetSingletonInstances = true;
+
+    /**
+     * @test
+     */
+    public function configuredContentIdIsUsed(): void
+    {
+        $processorConfiguration = ['contentId' => 1];
+        $contentObjectRenderer = $this->getMockBuilder(ContentObjectRenderer::class)->disableOriginalConstructor()->getMock();
+        $contentObjectRenderer->expects($this->never())->method('stdWrap');
+        $context = $this->getMockBuilder(Context::class)->getMock();
+        $contentDataProcessor = $this->getMockBuilder(ContentDataProcessor::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory = $this->getMockBuilder(FrontendContainerFactory::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory->expects($this->once())->method('buildContainer')->with(
+            $contentObjectRenderer, $context, 1
+        )->willReturn(new Container([], []));
+        $containerProcessor = new ContainerProcessor($contentDataProcessor, $context, $frontendContainerFactory);
+        $containerProcessor->process($contentObjectRenderer, [], $processorConfiguration, []);
+    }
+
+    /**
+     * @test
+     */
+    public function configuredContentIdStdWrapIsUsed(): void
+    {
+        $processorConfiguration = ['contentId' => 1, 'contentId.' => 'foo'];
+        $contentObjectRenderer = $this->getMockBuilder(ContentObjectRenderer::class)->disableOriginalConstructor()->getMock();
+        $contentObjectRenderer->expects($this->once())->method('stdWrap')->with(1, 'foo')->willReturn(2);
+        $context = $this->getMockBuilder(Context::class)->getMock();
+        $contentDataProcessor = $this->getMockBuilder(ContentDataProcessor::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory = $this->getMockBuilder(FrontendContainerFactory::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory->expects($this->once())->method('buildContainer')->with(
+            $contentObjectRenderer, $context, 2
+        )->willReturn(new Container([], []));
+        $containerProcessor = new ContainerProcessor($contentDataProcessor, $context, $frontendContainerFactory);
+        $containerProcessor->process($contentObjectRenderer, [], $processorConfiguration, []);
+    }
+
+    /**
+     * @test
+     */
+    public function canBeCalledWithoutContentId(): void
+    {
+        $processorConfiguration = ['contentId.' => 'foo'];
+        $contentObjectRenderer = $this->getMockBuilder(ContentObjectRenderer::class)->disableOriginalConstructor()->getMock();
+        $contentObjectRenderer->expects($this->once())->method('stdWrap')->with('', 'foo')->willReturn(2);
+        $context = $this->getMockBuilder(Context::class)->getMock();
+        $contentDataProcessor = $this->getMockBuilder(ContentDataProcessor::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory = $this->getMockBuilder(FrontendContainerFactory::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory->expects($this->once())->method('buildContainer')->with(
+            $contentObjectRenderer, $context, 2
+        )->willReturn(new Container([], []));
+        $containerProcessor = new ContainerProcessor($contentDataProcessor, $context, $frontendContainerFactory);
+        $containerProcessor->process($contentObjectRenderer, [], $processorConfiguration, []);
+    }
+
+    /**
+     * @test
+     */
+    public function nullIsUsedForFactoryIfNoContentIdIsGiven(): void
+    {
+        $processorConfiguration = [];
+        $contentObjectRenderer = $this->getMockBuilder(ContentObjectRenderer::class)->disableOriginalConstructor()->getMock();
+        $contentObjectRenderer->expects($this->never())->method('stdWrap');
+        $context = $this->getMockBuilder(Context::class)->getMock();
+        $contentDataProcessor = $this->getMockBuilder(ContentDataProcessor::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory = $this->getMockBuilder(FrontendContainerFactory::class)->disableOriginalConstructor()->getMock();
+        $frontendContainerFactory->expects($this->once())->method('buildContainer')->with(
+            $contentObjectRenderer, $context, null
+        )->willReturn(new Container([], []));
+        $containerProcessor = new ContainerProcessor($contentDataProcessor, $context, $frontendContainerFactory);
+        $containerProcessor->process($contentObjectRenderer, [], $processorConfiguration, []);
+    }
+
+}