diff --git a/.gitattributes b/.gitattributes
index 37f66b6..366ae55 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1,4 @@
 .gitattributes export-ignore
 .gitignore export-ignore
+phpcs.xml export-ignore
+phpstan.neon export-ignore
diff --git a/composer.json b/composer.json
index 0d183d7..077c2c9 100644
--- a/composer.json
+++ b/composer.json
@@ -19,6 +19,24 @@
 		"nette/di": "^3.0",
 		"nette/utils": "^3.2"
 	},
+	"require-dev": {
+		"php-parallel-lint/php-parallel-lint": "^1.3",
+		"php-parallel-lint/php-console-highlighter": "^0.5.0",
+		"phpstan/phpstan": "^0.12.99",
+		"phpstan/phpstan-nette": "^0.12.21",
+		"spaze/coding-standard": "^0.0",
+		"spaze/encryption": "^0.4.0"
+	},
+	"scripts": {
+		"lint": "vendor/bin/parallel-lint --colors src/",
+		"phpcs": "vendor/bin/phpcs src/",
+		"phpstan": "vendor/phpstan/phpstan/phpstan --ansi analyse --configuration phpstan.neon",
+		"test": [
+			"@lint",
+			"@phpcs",
+			"@phpstan"
+		]
+	},
 	"autoload": {
 		"classmap": ["src/"]
 	},
diff --git a/phpcs.xml b/phpcs.xml
new file mode 100644
index 0000000..d5af649
--- /dev/null
+++ b/phpcs.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0"?>
+<ruleset name="MysqlSessionHandler">
+	<arg name="extensions" value="php"/>
+	<arg name="cache"/>
+	<arg name="colors"/>
+	<arg value="s"/>
+	<arg value="p"/>
+	<rule ref="vendor/spaze/coding-standard/src/ruleset.xml"/>
+</ruleset>
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..24b4d98
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,8 @@
+parameters:
+	paths:
+		- src
+	level: 7
+
+includes:
+	- vendor/phpstan/phpstan-nette/extension.neon
+	- vendor/phpstan/phpstan-nette/rules.neon
diff --git a/src/DI/MysqlSessionHandlerExtension.php b/src/DI/MysqlSessionHandlerExtension.php
index 8259d5c..d70cb30 100644
--- a/src/DI/MysqlSessionHandlerExtension.php
+++ b/src/DI/MysqlSessionHandlerExtension.php
@@ -9,7 +9,7 @@
 class MysqlSessionHandlerExtension extends CompilerExtension
 {
 
-	private $defaults = [
+	private array $defaults = [
 		'tableName' => 'sessions',
 		'lockTimeout' => 5,
 		'unchangedUpdateDelay' => 300,
diff --git a/src/MysqlSessionHandler.php b/src/MysqlSessionHandler.php
index 810c598..65e3fc0 100644
--- a/src/MysqlSessionHandler.php
+++ b/src/MysqlSessionHandler.php
@@ -18,35 +18,30 @@ class MysqlSessionHandler implements SessionHandlerInterface
 
 	use SmartObject;
 
-	/** @var string */
-	private $tableName;
 
-	/** @var integer */
-	private $lockTimeout = 5;
+	private Context $context;
 
-	/** @var integer */
-	private $unchangedUpdateDelay = 300;
+	private ?StaticKeyEncryption $encryptionService = null;
 
-	/** @var Context */
-	private $context;
+	private string $tableName;
 
-	/** @var string */
-	private $lockId;
+	private int $lockTimeout = 5;
+
+	private int $unchangedUpdateDelay = 300;
+
+	private ?string $lockId = null;
 
 	/** @var string[] */
-	private $idHashes = [];
+	private array $idHashes = [];
 
-	/** @var ActiveRow */
-	private $row;
+	/** @var ActiveRow{data:string, timestamp:int}|null */
+	private ?ActiveRow $row;
 
 	/** @var string[] */
-	private $data = [];
+	private array $data = [];
 
 	/** @var mixed[] */
-	private $additionalData = [];
-
-	/** @var StaticKeyEncryption */
-	private $encryptionService;
+	private array $additionalData = [];
 
 	/**
 	 * Occurs before the data is written to session.
@@ -108,8 +103,11 @@ private function hash(string $id, bool $rawOutput = true): string
 	private function lock(): void
 	{
 		if ($this->lockId === null) {
-			$this->lockId = $this->hash(\session_id(), false);
-			$this->context->query('SELECT GET_LOCK(?, ?) as `lock`', $this->lockId, $this->lockTimeout);
+			$sessionId = \session_id();
+			if ($sessionId) {
+				$this->lockId = $this->hash($sessionId, false);
+				$this->context->query('SELECT GET_LOCK(?, ?) as `lock`', $this->lockId, $this->lockTimeout);
+			}
 		}
 	}
 
@@ -128,7 +126,7 @@ private function unlock(): void
 	/**
 	 * @param string $savePath
 	 * @param string $name
-	 * @return boolean
+	 * @return bool
 	 */
 	public function open($savePath, $name): bool
 	{
@@ -146,7 +144,7 @@ public function close(): bool
 
 	/**
 	 * @param string $sessionId
-	 * @return boolean
+	 * @return bool
 	 */
 	public function destroy($sessionId): bool
 	{
@@ -178,7 +176,7 @@ public function read($sessionId): string
 	/**
 	 * @param string $sessionId
 	 * @param string $sessionData
-	 * @return boolean
+	 * @return bool
 	 */
 	public function write($sessionId, $sessionData): bool
 	{
@@ -191,7 +189,8 @@ public function write($sessionId, $sessionData): bool
 				$sessionData = $this->encryptionService->encrypt($sessionData);
 			}
 			$this->onBeforeDataWrite();
-			if ($row = $this->context->table($this->tableName)->get($hashedSessionId)) {
+			$row = $this->context->table($this->tableName)->get($hashedSessionId);
+			if ($row) {
 				$row->update([
 					'timestamp' => $time,
 					'data' => $sessionData,
@@ -203,7 +202,7 @@ public function write($sessionId, $sessionData): bool
 					'data' => $sessionData,
 				] + $this->additionalData);
 			}
-		} elseif ($this->unchangedUpdateDelay === 0 || $time - $this->row->timestamp > $this->unchangedUpdateDelay) {
+		} elseif (($this->unchangedUpdateDelay === 0 || $time - $this->row->timestamp > $this->unchangedUpdateDelay) && $this->row) {
 			// Optimization: When data has not been changed, only update
 			// the timestamp after a configured delay, if any.
 			$this->row->update([
@@ -216,8 +215,8 @@ public function write($sessionId, $sessionData): bool
 
 
 	/**
-	 * @param integer $maxLifeTime
-	 * @return boolean
+	 * @param int $maxLifeTime
+	 * @return bool
 	 */
 	public function gc($maxLifeTime): bool
 	{