diff --git a/Message/HeaderAbstract.php b/Message/HeaderAbstract.php
index bcc256a45..f64bf8bc8 100644
--- a/Message/HeaderAbstract.php
+++ b/Message/HeaderAbstract.php
@@ -199,11 +199,11 @@ abstract class HeaderAbstract
      * @param string $value     Header value
      * @param bool   $overwrite Overwrite if key already exists
      * 
-     * @return void
+     * @return bool
      *
      * @since  1.0.0
      */
-    abstract public function set(string $key, string $value, bool $overwrite = false) : void;
+    abstract public function set(string $key, string $value, bool $overwrite = false) : bool;
 
     /**
      * Get header by key.
diff --git a/Utils/Parser/Markdown/Markdown.php b/Utils/Parser/Markdown/Markdown.php
index fe1a3840b..c28ba2b3c 100644
--- a/Utils/Parser/Markdown/Markdown.php
+++ b/Utils/Parser/Markdown/Markdown.php
@@ -29,7 +29,7 @@ class Markdown
     /**
      * Blocktypes.
      *
-     * @var string[]
+     * @var string[][]
      * @since 1.0.0
      */
     protected static $blockTypes = [
@@ -138,7 +138,7 @@ class Markdown
     /**
      * Inline identifiers.
      *
-     * @var string[]
+     * @var string[][]
      * @since 1.0.0
      */
     protected static $inlineTypes = [
@@ -414,7 +414,7 @@ class Markdown
      *
      * @since  1.0.0
      */
-    protected static function blockCodeComplete(array $block) : array
+    protected static function blockCodeComplete(?array $block) : ?array
     {
         return $block;
     }
@@ -498,7 +498,7 @@ class Markdown
      *
      * @since  1.0.0
      */
-    protected static function blockFencedCodeComplete(array $block) : array
+    protected static function blockFencedCodeComplete(?array $block) : ?array
     {
         return $block;
     }
@@ -635,6 +635,8 @@ class Markdown
 
             return $block;
         }
+
+        return null;
     }
 
     /**
@@ -690,6 +692,8 @@ class Markdown
 
             return $block;
         }
+
+        return null;
     }
 
     /**
@@ -857,6 +861,8 @@ class Markdown
 
             return $block;
         }
+
+        return null;
     }
 
     /**
@@ -934,7 +940,7 @@ class Markdown
      *
      * @param string $text Line of text
      * 
-     * @return array
+     * @return string
      *
      * @since  1.0.0
      */
@@ -1475,7 +1481,7 @@ class Markdown
      * Escape html elements
      * 
      * @param string $text        Text to escape
-     * @param string $allowQuotes Are quotes allowed
+     * @param bool   $allowQuotes Are quotes allowed
      * 
      * @return string
      *
diff --git a/tests/DataStorage/Database/DatabasePoolTest.php b/tests/DataStorage/Database/DatabasePoolTest.php
index 3a5a4b94a..85ceac907 100644
--- a/tests/DataStorage/Database/DatabasePoolTest.php
+++ b/tests/DataStorage/Database/DatabasePoolTest.php
@@ -14,6 +14,7 @@
 namespace phpOMS\tests\DataStorage\Database;
 
 use phpOMS\DataStorage\Database\Connection\MysqlConnection;
+use phpOMS\DataStorage\Database\Connection\NullConnection;
 use phpOMS\DataStorage\Database\DatabaseStatus;
 use phpOMS\DataStorage\Database\DatabasePool;
 
@@ -37,13 +38,13 @@ class DatabasePoolTest extends \PHPUnit\Framework\TestCase
         self::assertFalse($dbPool->create('core', $GLOBALS['CONFIG']['db']['core']['masters']['admin']));
 
         self::assertInstanceOf('\phpOMS\DataStorage\Database\Connection\ConnectionAbstract', $dbPool->get());
-        self::assertNull($dbPool->get('doesNotExist'));
+        self::assertInstanceOf('\phpOMS\DataStorage\Database\Connection\NullConnection', $dbPool->get('doesNotExist'));
         self::assertEquals($dbPool->get('core'), $dbPool->get());
 
         self::assertFalse($dbPool->remove('cores'));
         self::assertTrue($dbPool->remove('core'));
 
-        self::assertNull($dbPool->get());
+        self::assertInstanceOf('\phpOMS\DataStorage\Database\Connection\NullConnection', $dbPool->get());
 
         self::assertTrue($dbPool->add('core', new MysqlConnection($GLOBALS['CONFIG']['db']['core']['masters']['admin'])));
         self::assertFalse($dbPool->add('core', new MysqlConnection($GLOBALS['CONFIG']['db']['core']['masters']['admin'])));
diff --git a/tests/Message/HeaderAbstractTest.php b/tests/Message/HeaderAbstractTest.php
index 0989d77c5..5779f471f 100644
--- a/tests/Message/HeaderAbstractTest.php
+++ b/tests/Message/HeaderAbstractTest.php
@@ -34,9 +34,9 @@ class HeaderAbstractTest extends \PHPUnit\Framework\TestCase
                 return '1';
             }
 
-            public function set(string $key, string $value, bool $overwrite = false) : void
+            public function set(string $key, string $value, bool $overwrite = false) : bool
             {
-
+                return true;
             }
 
             public function get(string $key) : array