diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..b921988
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,8 @@
+parameters:
+  level: 8
+  ignoreErrors:
+    #- message: '#Parameter \#1 \$data of static method kbATeam\\DataProtection\\SecureSearch::encrypt\(\) expects string, int given.#'
+    #  path: tests/SecureSearchTest.php
+  paths:
+    - src/
+    - tests/
diff --git a/src/Log/Engine/GraylogLog.php b/src/Log/Engine/GraylogLog.php
index 2f930e6..0bbf535 100644
--- a/src/Log/Engine/GraylogLog.php
+++ b/src/Log/Engine/GraylogLog.php
@@ -143,7 +143,7 @@ public function __construct($config = [])
      *
      * @param mixed   $level
      * @param string  $message
-     * @param array $context
+     * @param array<mixed> $context
      *
      * @return void
      *
@@ -259,6 +259,7 @@ protected function createMessage(string $level, string $message): GelfMessage
         /**
          * Create a debug backtrace.
          */
+        $trace = null;
         if ($add_file_and_line || $append_backtrace) {
             $trace = new ClassicBacktrace(
                 $this->getConfig('trace_level_offset'),
@@ -270,7 +271,7 @@ protected function createMessage(string $level, string $message): GelfMessage
          * In case the log didn't happen in memory (like with reflections), add
          * the filename and line to the message.
          */
-        if ($add_file_and_line && $trace->lastStep('file') !== null) {
+        if ($add_file_and_line && is_object($trace) && $trace->lastStep('file') !== null) {
             $gelfMessage->setAdditional('file', $trace->lastStep('file'));
             $gelfMessage->setAdditional('line', $trace->lastStep('line'));
         }
@@ -291,7 +292,7 @@ protected function createMessage(string $level, string $message): GelfMessage
         /**
          * Append backtrace in case it's not already in the message.
          */
-        if ($append_backtrace) {
+        if ($append_backtrace && is_object($trace)) {
             /**
              * Append backtrace to message.
              */
@@ -302,9 +303,13 @@ protected function createMessage(string $level, string $message): GelfMessage
         /**
          * Set function output as additional field.
          */
-        foreach ($this->getConfig('additional', []) as $key => $function) {
-            if (is_callable($function)) {
-                $gelfMessage->setAdditional($key, (string)$function());
+
+        $configStack = $this->getConfig('additional', []);
+        if (is_array($configStack)) {
+            foreach ($configStack as $key => $function) {
+                if (is_callable($function) && is_string($key)) {
+                    $gelfMessage->setAdditional($key, (string)$function());
+                }
             }
         }
 
@@ -321,7 +326,7 @@ protected function createMessage(string $level, string $message): GelfMessage
             return $gelfMessage->setShortMessage($shortMessage);
         }
         return $gelfMessage
-            ->setShortMessage($shortMessage)
+            ->setShortMessage((string)$shortMessage)
             ->setFullMessage($message);
     }
 }
diff --git a/tests/GraylogLogTest.php b/tests/GraylogLogTest.php
index 05822c3..9f2055c 100644
--- a/tests/GraylogLogTest.php
+++ b/tests/GraylogLogTest.php
@@ -12,6 +12,7 @@
 use InvalidArgumentException;
 use kbATeam\CakePhpGraylog\Log\Engine\GraylogLog;
 use LogicException;
+use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\Exception;
 use PHPUnit\Framework\TestCase;
 use Psr\Log\LoggerInterface;
@@ -27,39 +28,41 @@ class GraylogLogTest extends TestCase
     /**
      * Test inheritance chain to ensure this test deals with the correct class.
      * @throws Exception
+     * @return void
      */
     public function testInheritance()
     {
         $log = new PublicGraylogLog();
-        static::assertInstanceOf(LoggerInterface::class, $log);
-        static::assertInstanceOf(BaseLog::class, $log);
-        static::assertInstanceOf(GraylogLog::class, $log);
+        $this->assertInstanceOf(LoggerInterface::class, $log);
+        $this->assertInstanceOf(BaseLog::class, $log);
+        $this->assertInstanceOf(GraylogLog::class, $log);
     }
 
     /**
      * Test default config settings to ensure that later settings are different.
-     * @throws PHPUnit_Framework_AssertionFailedError
+     * @throws AssertionFailedError
      * @throws InvalidArgumentException
+     * @return void
      */
     public function testDefaultConfig()
     {
         $log = new PublicGraylogLog();
-        static::assertSame('udp', $log->getMyConfig('scheme'));
-        static::assertSame('127.0.0.1', $log->getMyConfig('host'));
-        static::assertSame(12201, $log->getMyConfig('port'));
-        static::assertSame(UdpTransport::CHUNK_SIZE_LAN, $log->getMyConfig('chunk_size'));
-        static::assertNull($log->getMyConfig('ssl_options'));
-        static::assertSame('CakePHP', $log->getMyConfig('facility'));
-        static::assertFalse($log->getMyConfig('append_backtrace'));
-        static::assertFalse($log->getMyConfig('append_session'));
-        static::assertFalse($log->getMyConfig('append_post'));
-        static::assertSame([
+        $this->assertSame('udp', $log->getMyConfig('scheme'));
+        $this->assertSame('127.0.0.1', $log->getMyConfig('host'));
+        $this->assertSame(12201, $log->getMyConfig('port'));
+        $this->assertSame(UdpTransport::CHUNK_SIZE_LAN, $log->getMyConfig('chunk_size'));
+        $this->assertNull($log->getMyConfig('ssl_options'));
+        $this->assertSame('CakePHP', $log->getMyConfig('facility'));
+        $this->assertFalse($log->getMyConfig('append_backtrace'));
+        $this->assertFalse($log->getMyConfig('append_session'));
+        $this->assertFalse($log->getMyConfig('append_post'));
+        $this->assertSame([
             'password',
             'new_password',
             'old_password',
             'current_password'
         ], $log->getMyConfig('password_keys'));
-        static::assertSame([
+        $this->assertSame([
             LogLevel::EMERGENCY,
             LogLevel::ALERT,
             LogLevel::CRITICAL,
@@ -73,18 +76,19 @@ public function testDefaultConfig()
 
     /**
      * Test that valid ssl options are being added to the configuration.
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
      * @throws InvalidArgumentException
+     * @return void
      */
     public function testValidSslOptions()
     {
         $log = new PublicGraylogLog(['ssl_options' => new SslOptions()]);
-        static::assertInstanceOf(SslOptions::class, $log->getMyConfig('ssl_options'));
+        $this->assertInstanceOf(SslOptions::class, $log->getMyConfig('ssl_options'));
     }
 
     /**
      * Provide invalid values for ssl options.
-     * @return array
+     * @return array<int, array<mixed>>
      */
     public static function provideInvalidSslOptions(): array
     {
@@ -105,16 +109,17 @@ public static function provideInvalidSslOptions(): array
      * @param mixed $option
      * @dataProvider provideInvalidSslOptions
      * @throws InvalidArgumentException
+     * @return void
      */
     public function testInvalidSslOptions($option)
     {
         $log = new PublicGraylogLog(['ssl_options' => $option]);
-        static::assertNull($log->getMyConfig('ssl_options'));
+        $this->assertNull($log->getMyConfig('ssl_options'));
     }
 
     /**
      * Data provider for connection URLs and their parsed values.
-     * @return array
+     * @return array<int,array<mixed>>
      */
     public static function provideConnectionUrl(): array
     {
@@ -134,30 +139,30 @@ public static function provideConnectionUrl(): array
      * @param int $port
      * @dataProvider provideConnectionUrl
      * @throws InvalidArgumentException
-     * @throws InvalidArgumentException
-     * @throws InvalidArgumentException
+     * @return void
      */
     public function testConnectionUrl(string $url, string $scheme, string $host, int $port)
     {
         $log = new PublicGraylogLog(['url' => $url]);
-        static::assertSame($scheme, $log->getMyConfig('scheme'));
-        static::assertSame($host, $log->getMyConfig('host'));
-        static::assertSame($port, $log->getMyConfig('port'));
+        $this->assertSame($scheme, $log->getMyConfig('scheme'));
+        $this->assertSame($host, $log->getMyConfig('host'));
+        $this->assertSame($port, $log->getMyConfig('port'));
     }
 
     /**
      * Test setting only certain log levels.
      * @throws InvalidArgumentException
+     * @return void
      */
     public function testSettingLogLevels()
     {
         $log = new PublicGraylogLog(['levels' => [LogLevel::ERROR, LogLevel::WARNING, 'i5A64FtlPt']]);
-        static::assertSame([LogLevel::ERROR, LogLevel::WARNING], $log->getMyConfig('levels'));
+        $this->assertSame([LogLevel::ERROR, LogLevel::WARNING], $log->getMyConfig('levels'));
     }
 
     /**
      * Data provider of invalid log levels.
-     * @return array
+     * @return array<mixed>
      */
     public static function provideInvalidLogLevels(): array
     {
@@ -177,13 +182,14 @@ public static function provideInvalidLogLevels(): array
      * Test setting only invalid log levels resulting in enabling all log levels.
      * @param mixed $levels
      * @dataProvider provideInvalidLogLevels
+     * @return void
      */
     public function testInvalidLogLevels($levels)
     {
         $this->expectException(\TypeError::class);
 
         $log = new PublicGraylogLog(['levels' => $levels]);
-        static::assertSame([
+        $this->assertSame([
             LogLevel::EMERGENCY,
             LogLevel::ALERT,
             LogLevel::CRITICAL,
@@ -198,10 +204,8 @@ public function testInvalidLogLevels($levels)
     /**
      * Test creating a GELF message with default settings.
      * @throws RuntimeException
-     * @throws PHPUnit_Framework_Exception
-     * @throws PHPUnit_Framework_Exception
-     * @throws PHPUnit_Framework_Exception
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testCreatingLongMessage()
     {
@@ -221,58 +225,61 @@ public function testCreatingLongMessage()
             'append_post' => true
         ]);
         $message = $log->createMessage(LogLevel::DEBUG, 'mnfiXQoolR');
-        static::assertInstanceOf(GelfMessage::class, $message);
-        static::assertSame('CakePHP', $message->getAdditional('facility'));
-        static::assertSame(LogLevel::DEBUG, $message->getLevel());
-        static::assertSame('mnfiXQoolR', $message->getShortMessage());
-        static::assertCount(3, $message->getAllAdditionals());
-        static::assertStringContainsString('POST:', $message->getFullMessage());
-        static::assertStringContainsString('Session:', $message->getFullMessage());
-        static::assertStringContainsString('Trace:', $message->getFullMessage());
+        $this->assertInstanceOf(GelfMessage::class, $message);
+        $this->assertSame('CakePHP', $message->getAdditional('facility'));
+        $this->assertSame(LogLevel::DEBUG, $message->getLevel());
+        $this->assertSame('mnfiXQoolR', $message->getShortMessage());
+        $this->assertCount(3, $message->getAllAdditionals());
+        $this->assertStringContainsString('POST:', (string)$message->getFullMessage());
+        $this->assertStringContainsString('Session:', (string)$message->getFullMessage());
+        $this->assertStringContainsString('Trace:', (string)$message->getFullMessage());
         unset($_POST);
     }
 
     /**
      * Test creating a GELF message without any appended debug information.
      * @throws RuntimeException
+     * @return void
      */
     public function testShortMessage()
     {
         $log = new PublicGraylogLog();
         $message = $log->createMessage(LogLevel::ALERT, 'oIEUMcF1Ce');
-        static::assertSame(LogLevel::ALERT, $message->getLevel());
-        static::assertSame('oIEUMcF1Ce', $message->getShortMessage());
-        static::assertNull($message->getFullMessage());
+        $this->assertSame(LogLevel::ALERT, $message->getLevel());
+        $this->assertSame('oIEUMcF1Ce', $message->getShortMessage());
+        $this->assertNull($message->getFullMessage());
     }
 
     /**
      * Test getting a UDP transport class from default configuration.
      * @throws InvalidArgumentException
      * @throws LogicException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testUdpTransport()
     {
         $log = new PublicGraylogLog(['ignore_transport_errors' => false]);
         $transport = $log->getTransport();
-        static::assertInstanceOf(UdpTransport::class, $transport);
+        $this->assertInstanceOf(UdpTransport::class, $transport);
         /**
          * Assert that we actually get the same instance.
          */
-        static::assertSame($transport, $log->getTransport());
+        $this->assertSame($transport, $log->getTransport());
     }
 
     /**
      * Test getting a TCP transport class from default configuration.
      * @throws InvalidArgumentException
      * @throws LogicException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testTcpTransport()
     {
         $log = new PublicGraylogLog(['scheme' => 'tcp', 'ignore_transport_errors' => false]);
         $transport = $log->getTransport();
-        static::assertInstanceOf(TcpTransport::class, $transport);
+        $this->assertInstanceOf(TcpTransport::class, $transport);
     }
 
     /**
@@ -280,20 +287,22 @@ public function testTcpTransport()
      * @return void
      * @throws InvalidArgumentException
      * @throws LogicException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testTransportWrapper()
     {
         $log = new PublicGraylogLog();
         $transport = $log->getTransport();
-        static::assertInstanceOf(IgnoreErrorTransportWrapper::class, $transport);
+        $this->assertInstanceOf(IgnoreErrorTransportWrapper::class, $transport);
     }
 
     /**
      * Test getting an exception from an invalid scheme.
      * @throws InvalidArgumentException
      * @throws LogicException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testInvalidScheme()
     {
@@ -307,23 +316,25 @@ public function testInvalidScheme()
      * Test getting a publisher class from default configuration.
      * @throws InvalidArgumentException
      * @throws LogicException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testPublisher()
     {
         $log = new PublicGraylogLog();
         $publisher = $log->getPublisher();
-        static::assertInstanceOf(Publisher::class, $publisher);
+        $this->assertInstanceOf(Publisher::class, $publisher);
         /**
          * Assert that we actually get the same instance.
          */
-        static::assertSame($publisher, $log->getPublisher());
+        $this->assertSame($publisher, $log->getPublisher());
     }
 
     /**
      * Test adding additional field.
      * @throws RuntimeException
      * @throws RuntimeException
+     * @return void
      */
     public function testAddingAdditionalFields()
     {
@@ -335,16 +346,17 @@ public function testAddingAdditionalFields()
             ]
         ]);
         $message = $log->createMessage(LogLevel::INFO, 'Cy6BWVa5E0');
-        static::assertSame(LogLevel::INFO, $message->getLevel());
-        static::assertSame('Cy6BWVa5E0', $message->getShortMessage());
-        static::assertNull($message->getFullMessage());
-        static::assertSame('MSg9BrM4DG', $message->getAdditional('bmC5B27F3R'));
+        $this->assertSame(LogLevel::INFO, $message->getLevel());
+        $this->assertSame('Cy6BWVa5E0', $message->getShortMessage());
+        $this->assertNull($message->getFullMessage());
+        $this->assertSame('MSg9BrM4DG', $message->getAdditional('bmC5B27F3R'));
     }
 
     /**
      * Test creating a GELF message with all flags enabled.
      * @throws RuntimeException
-     * @throws PHPUnit_Framework_Exception
+     * @throws Exception
+     * @return void
      */
     public function testNoEmptyPostInLongMessage()
     {
@@ -356,11 +368,11 @@ public function testNoEmptyPostInLongMessage()
             'append_post' => true
         ]);
         $message = $log->createMessage(LogLevel::CRITICAL, 'oP6MkuApf9');
-        static::assertInstanceOf(GelfMessage::class, $message);
-        static::assertSame('CakePHP', $message->getAdditional('facility'));
-        static::assertSame(LogLevel::CRITICAL, $message->getLevel());
-        static::assertSame('oP6MkuApf9', $message->getShortMessage());
-        static::assertCount(3, $message->getAllAdditionals());
-        static::assertNull($message->getFullMessage());
+        $this->assertInstanceOf(GelfMessage::class, $message);
+        $this->assertSame('CakePHP', $message->getAdditional('facility'));
+        $this->assertSame(LogLevel::CRITICAL, $message->getLevel());
+        $this->assertSame('oP6MkuApf9', $message->getShortMessage());
+        $this->assertCount(3, $message->getAllAdditionals());
+        $this->assertNull($message->getFullMessage());
     }
 }
diff --git a/tests/GraylogWriteTest.php b/tests/GraylogWriteTest.php
index c788c72..efc5a3d 100644
--- a/tests/GraylogWriteTest.php
+++ b/tests/GraylogWriteTest.php
@@ -16,7 +16,7 @@
     class Publisher
     {
         /**
-         * @var TransportInterface
+         * @var TransportInterface|null
          */
         public $transport;
 
@@ -37,6 +37,7 @@ public function __construct(TransportInterface $transport = null)
         /**
          * @param MessageInterface $message
          * @noinspection PhpUnused
+         * @return void
          */
         public function publish(MessageInterface $message)
         {
@@ -51,6 +52,7 @@ public function publish(MessageInterface $message)
     use Gelf\Transport\UdpTransport;
     use InvalidArgumentException;
     use LogicException;
+    use PHPUnit\Framework\Exception;
     use PHPUnit\Framework\TestCase;
     use PHPUnit_Framework_Exception;
     use PHPUnit_Framework_TestCase;
@@ -63,10 +65,11 @@ class GraylogWriteTest extends TestCase
     {
         /**
          * Test writing a message using a fake publisher class.
-         * @throws PHPUnit_Framework_Exception
+         * @throws Exception
          * @throws InvalidArgumentException
          * @throws LogicException
          * @throws RuntimeException
+         * @return void
          */
         public function testWriteUsingFakePublisher()
         {