diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 276e466..82b57cb 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,7 +13,7 @@ jobs:
     tests:
         uses: janpecha/actions/.github/workflows/nette-tester-library.yml@master
         with:
-            phpVersions: '["5.6", "7.0", "7.1", "7.2", "7.3", "7.4", "8.0", "8.1", "8.2", "8.3"]'
+            phpVersions: '["7.4", "8.0", "8.1", "8.2", "8.3", "8.4"]'
             lowestDependencies: true
 
     coding-style:
diff --git a/code-checker.php b/code-checker.php
index 96eef7d..7a02154 100644
--- a/code-checker.php
+++ b/code-checker.php
@@ -1,8 +1,13 @@
 <?php
 
 return function (JP\CodeChecker\CheckerConfig $config) {
-	$config->setPhpVersion(new JP\CodeChecker\Version('5.6.0'));
+	$config->setPhpVersion(new JP\CodeChecker\Version('7.4.0'));
 	$config->addPath('./src');
 	$config->addPath('./tests');
+	$config->setParameters([
+		'php' => [
+			'strictTypes' => FALSE,
+		],
+	]);
 	JP\CodeChecker\Sets\CzProjectMinimum::configure($config);
 };
diff --git a/composer.json b/composer.json
index b6289ca..742667c 100644
--- a/composer.json
+++ b/composer.json
@@ -15,12 +15,12 @@
 		{"type": "other", "url": "https://www.janpecha.cz/donate/git-php/"}
 	],
 	"require": {
-		"php": ">=5.6.0"
+		"php": ">=7.4.0"
 	},
 	"autoload": {
 		"classmap": ["src/"]
 	},
 	"require-dev": {
-		"nette/tester": "^2.0"
+		"nette/tester": "^2.4"
 	}
 }
diff --git a/readme.md b/readme.md
index 88b031a..185cb3c 100644
--- a/readme.md
+++ b/readme.md
@@ -21,7 +21,7 @@ Installation
 composer require czproject/git-php
 ```
 
-Library requires PHP 5.6 or later and `git` client (path to Git must be in system variable `PATH`).
+Library requires PHP 7.4 or later and `git` client (path to Git must be in system variable `PATH`).
 
 Git installers:
 
diff --git a/src/CommandProcessor.php b/src/CommandProcessor.php
index 83372b3..7f57e4c 100644
--- a/src/CommandProcessor.php
+++ b/src/CommandProcessor.php
@@ -39,7 +39,7 @@ public function __construct($mode = self::MODE_DETECT)
 		 * @param  array<string, scalar>|NULL $env
 		 * @return string
 		 */
-		public function process($app, array $args, array $env = NULL)
+		public function process($app, array $args, ?array $env = NULL)
 		{
 			$cmd = [];
 
diff --git a/src/Git.php b/src/Git.php
index d4d562d..e23a192 100644
--- a/src/Git.php
+++ b/src/Git.php
@@ -9,7 +9,7 @@ class Git
 		protected $runner;
 
 
-		public function  __construct(IRunner $runner = NULL)
+		public function  __construct(?IRunner $runner = NULL)
 		{
 			$this->runner = $runner !== NULL ? $runner : new Runners\CliRunner;
 		}
@@ -32,7 +32,7 @@ public function open($directory)
 		 * @return GitRepository
 		 * @throws GitException
 		 */
-		public function init($directory, array $params = NULL)
+		public function init($directory, ?array $params = NULL)
 		{
 			if (is_dir("$directory/.git")) {
 				throw new GitException("Repo already exists in $directory.");
@@ -66,7 +66,7 @@ public function init($directory, array $params = NULL)
 		 * @return GitRepository
 		 * @throws GitException
 		 */
-		public function cloneRepository($url, $directory = NULL, array $params = NULL)
+		public function cloneRepository($url, $directory = NULL, ?array $params = NULL)
 		{
 			if ($directory !== NULL && is_dir("$directory/.git")) {
 				throw new GitException("Repo already exists in $directory.");
@@ -115,7 +115,7 @@ public function cloneRepository($url, $directory = NULL, array $params = NULL)
 		 * @param  array<string>|NULL $refs
 		 * @return bool
 		 */
-		public function isRemoteUrlReadable($url, array $refs = NULL)
+		public function isRemoteUrlReadable($url, ?array $refs = NULL)
 		{
 			$result = $this->runner->run($this->runner->getCwd(), [
 				'ls-remote',
@@ -139,7 +139,7 @@ public function isRemoteUrlReadable($url, array $refs = NULL)
 		 * @return RunnerResult
 		 * @throws GitException
 		 */
-		private function run($cwd, array $args, array $env = NULL)
+		private function run($cwd, array $args, ?array $env = NULL)
 		{
 			$result = $this->runner->run($cwd, $args, $env);
 
diff --git a/src/GitRepository.php b/src/GitRepository.php
index cd8d5fa..9855007 100644
--- a/src/GitRepository.php
+++ b/src/GitRepository.php
@@ -16,7 +16,7 @@ class GitRepository
 		 * @param  string $repository
 		 * @throws GitException
 		 */
-		public function __construct($repository, IRunner $runner = NULL)
+		public function __construct($repository, ?IRunner $runner = NULL)
 		{
 			if (basename($repository) === '.git') {
 				$repository = dirname($repository);
@@ -466,7 +466,7 @@ public function hasChanges()
 		 * @return static
 		 * @throws GitException
 		 */
-		public function pull($remote = NULL, array $options = NULL)
+		public function pull($remote = NULL, ?array $options = NULL)
 		{
 			$this->run('pull', $options, '--end-of-options', $remote);
 			return $this;
@@ -480,7 +480,7 @@ public function pull($remote = NULL, array $options = NULL)
 		 * @return static
 		 * @throws GitException
 		 */
-		public function push($remote = NULL, array $options = NULL)
+		public function push($remote = NULL, ?array $options = NULL)
 		{
 			$this->run('push', $options, '--end-of-options', $remote);
 			return $this;
@@ -494,7 +494,7 @@ public function push($remote = NULL, array $options = NULL)
 		 * @return static
 		 * @throws GitException
 		 */
-		public function fetch($remote = NULL, array $options = NULL)
+		public function fetch($remote = NULL, ?array $options = NULL)
 		{
 			$this->run('fetch', $options, '--end-of-options', $remote);
 			return $this;
@@ -509,7 +509,7 @@ public function fetch($remote = NULL, array $options = NULL)
 		 * @return static
 		 * @throws GitException
 		 */
-		public function addRemote($name, $url, array $options = NULL)
+		public function addRemote($name, $url, ?array $options = NULL)
 		{
 			$this->run('remote', 'add', $options, '--end-of-options', $name, $url);
 			return $this;
@@ -551,7 +551,7 @@ public function removeRemote($name)
 		 * @return static
 		 * @throws GitException
 		 */
-		public function setRemoteUrl($name, $url, array $options = NULL)
+		public function setRemoteUrl($name, $url, ?array $options = NULL)
 		{
 			$this->run('remote', 'set-url', $options, '--end-of-options', $name, $url);
 			return $this;
@@ -590,10 +590,11 @@ public function run(...$args)
 
 		/**
 		 * @param  array<mixed> $args
+		 * @param  (callable(string $value): (string|FALSE))|NULL $filter
 		 * @return string[]|NULL
 		 * @throws GitException
 		 */
-		protected function extractFromCommand(array $args, callable $filter = NULL)
+		protected function extractFromCommand(array $args, ?callable $filter = NULL)
 		{
 			$result = $this->run(...$args);
 			$output = $result->getOutput();
diff --git a/src/IRunner.php b/src/IRunner.php
index 453ff68..3323838 100644
--- a/src/IRunner.php
+++ b/src/IRunner.php
@@ -11,7 +11,7 @@ interface IRunner
 		 * @param  array<string, scalar>|NULL $env
 		 * @return RunnerResult
 		 */
-		function run($cwd, array $args, array $env = NULL);
+		function run($cwd, array $args, ?array $env = NULL);
 
 
 		/**
diff --git a/src/Runners/CliRunner.php b/src/Runners/CliRunner.php
index 462e61c..63c9da6 100644
--- a/src/Runners/CliRunner.php
+++ b/src/Runners/CliRunner.php
@@ -30,7 +30,7 @@ public function __construct($gitBinary = 'git')
 		/**
 		 * @return RunnerResult
 		 */
-		public function run($cwd, array $args, array $env = NULL)
+		public function run($cwd, array $args, ?array $env = NULL)
 		{
 			if (!is_dir($cwd)) {
 				throw new GitException("Directory '$cwd' not found");
@@ -52,6 +52,15 @@ public function run($cwd, array $args, array $env = NULL)
 				throw new GitException("Executing of command '$command' failed (directory $cwd).");
 			}
 
+			if (!(is_array($pipes)
+				&& isset($pipes[0], $pipes[1], $pipes[2])
+				&& is_resource($pipes[0])
+				&& is_resource($pipes[1])
+				&& is_resource($pipes[2])
+			)) {
+				throw new GitException("Invalid pipes for command '$command' failed (directory $cwd).");
+			}
+
 			// Reset output and error
 			stream_set_blocking($pipes[1], FALSE);
 			stream_set_blocking($pipes[2], FALSE);
diff --git a/src/Runners/MemoryRunner.php b/src/Runners/MemoryRunner.php
index 4982c9c..fb28523 100644
--- a/src/Runners/MemoryRunner.php
+++ b/src/Runners/MemoryRunner.php
@@ -49,7 +49,7 @@ public function setResult(array $args, array $env, $output, $errorOutput = [], $
 		/**
 		 * @return RunnerResult
 		 */
-		public function run($cwd, array $args, array $env = NULL)
+		public function run($cwd, array $args, ?array $env = NULL)
 		{
 			$cmd = $this->commandProcessor->process('git', $args, $env);
 
diff --git a/src/Runners/OldGitRunner.php b/src/Runners/OldGitRunner.php
index cb07136..ac85057 100644
--- a/src/Runners/OldGitRunner.php
+++ b/src/Runners/OldGitRunner.php
@@ -11,13 +11,13 @@ class OldGitRunner implements IRunner
 		private $runner;
 
 
-		public function __construct(IRunner $runner = NULL)
+		public function __construct(?IRunner $runner = NULL)
 		{
 			$this->runner = $runner !== NULL ? $runner : new CliRunner;
 		}
 
 
-		public function run($cwd, array $args, array $env = NULL)
+		public function run($cwd, array $args, ?array $env = NULL)
 		{
 			if (($key = array_search('--end-of-options', $args)) !== FALSE) {
 				unset($args[$key]);
diff --git a/src/exceptions.php b/src/exceptions.php
index b79bd39..1eac0d4 100644
--- a/src/exceptions.php
+++ b/src/exceptions.php
@@ -18,7 +18,7 @@ class GitException extends Exception
 		 * @param string $message
 		 * @param int $code
 		 */
-		public function __construct($message, $code = 0, \Exception $previous = NULL, RunnerResult $runnerResult = NULL)
+		public function __construct($message, $code = 0, ?\Exception $previous = NULL, ?RunnerResult $runnerResult = NULL)
 		{
 			parent::__construct($message, $code, $previous);
 			$this->runnerResult = $runnerResult;
diff --git a/tests/libs/AssertRunner.php b/tests/libs/AssertRunner.php
index db7d1e2..5538eb0 100644
--- a/tests/libs/AssertRunner.php
+++ b/tests/libs/AssertRunner.php
@@ -59,7 +59,7 @@ public function resetAsserts()
 		/**
 		 * @return RunnerResult
 		 */
-		public function run($cwd, array $args, array $env = NULL)
+		public function run($cwd, array $args, ?array $env = NULL)
 		{
 			if (empty($this->asserts)) {
 				throw new \CzProject\GitPhp\InvalidStateException('Missing asserts, use $runner->assert().');