diff --git a/Collector/Collector.php b/Collector/Collector.php
index 1a02d9c3..6258c1c0 100644
--- a/Collector/Collector.php
+++ b/Collector/Collector.php
@@ -62,7 +62,7 @@ public function getName()
      */
     public function activateStack(Stack $stack)
     {
-        if ($this->activeStack !== null) {
+        if (null !== $this->activeStack) {
             $stack->setParent($this->activeStack);
         }
 
@@ -141,7 +141,7 @@ public function getFailedStacks()
     public function getClients()
     {
         $stacks = array_filter($this->data['stacks'], function (Stack $stack) {
-            return $stack->getParent() === null;
+            return null === $stack->getParent();
         });
 
         return array_unique(array_map(function (Stack $stack) {
@@ -157,7 +157,7 @@ public function getClients()
     public function getClientRootStacks($client)
     {
         return array_filter($this->data['stacks'], function (Stack $stack) use ($client) {
-            return $stack->getClient() == $client && $stack->getParent() == null;
+            return $stack->getClient() == $client && null == $stack->getParent();
         });
     }
 
diff --git a/Collector/ProfileClient.php b/Collector/ProfileClient.php
index 5e92244d..2cb35930 100644
--- a/Collector/ProfileClient.php
+++ b/Collector/ProfileClient.php
@@ -77,7 +77,7 @@ public function sendAsyncRequest(RequestInterface $request)
     {
         $activateStack = true;
         $stack = $this->collector->getActiveStack();
-        if ($stack === null) {
+        if (null === $stack) {
             //When using a discovered client not wrapped in a PluginClient, we don't have a stack from StackPlugin. So
             //we create our own stack and activate it!
             $stack = new Stack('Default', $this->formatter->formatRequest($request));
@@ -120,7 +120,7 @@ public function sendAsyncRequest(RequestInterface $request)
     public function sendRequest(RequestInterface $request)
     {
         $stack = $this->collector->getActiveStack();
-        if ($stack === null) {
+        if (null === $stack) {
             //When using a discovered client not wrapped in a PluginClient, we don't have a stack from StackPlugin. So
             //we create our own stack but don't activate it.
             $stack = new Stack('Default', $this->formatter->formatRequest($request));
diff --git a/Collector/Stack.php b/Collector/Stack.php
index a5d467ce..815b1239 100644
--- a/Collector/Stack.php
+++ b/Collector/Stack.php
@@ -120,7 +120,7 @@ public function getParent()
     /**
      * @param Stack $parent
      */
-    public function setParent(Stack $parent)
+    public function setParent(self $parent)
     {
         $this->parent = $parent;
     }
diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 107e8c42..227df718 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -175,7 +175,7 @@ private function configureClients(ArrayNodeDefinition $root)
                 ->end()
                 ->validate()
                     ->ifTrue(function ($config) {
-                        return $config['factory'] === 'httplug.factory.auto' && !empty($config['config']);
+                        return 'httplug.factory.auto' === $config['factory'] && !empty($config['config']);
                     })
                     ->thenInvalid('If you want to use the "config" key you must also specify a valid "factory".')
                 ->end()
diff --git a/DependencyInjection/HttplugExtension.php b/DependencyInjection/HttplugExtension.php
index 1abaa70a..e8afe492 100644
--- a/DependencyInjection/HttplugExtension.php
+++ b/DependencyInjection/HttplugExtension.php
@@ -89,7 +89,7 @@ private function configureClients(ContainerBuilder $container, array $config)
         $clients = [];
 
         foreach ($config['clients'] as $name => $arguments) {
-            if ($first === null) {
+            if (null === $first) {
                 // Save the name of the first configured client.
                 $first = $name;
             }
@@ -99,7 +99,7 @@ private function configureClients(ContainerBuilder $container, array $config)
         }
 
         // If we have clients configured
-        if ($first !== null) {
+        if (null !== $first) {
             // If we do not have a client named 'default'
             if (!isset($config['clients']['default'])) {
                 // Alias the first client to httplug.client.default
@@ -153,6 +153,7 @@ private function configurePluginByName($name, Definition $definition, array $con
                     ->replaceArgument(0, new Reference($config['cache_pool']))
                     ->replaceArgument(1, new Reference($config['stream_factory']))
                     ->replaceArgument(2, $options);
+
                 break;
             case 'cookie':
                 $definition->replaceArgument(0, new Reference($config['cookie_jar']));
@@ -369,7 +370,7 @@ private function createUri(ContainerBuilder $container, $serviceId, $uri)
     private function configureAutoDiscoveryClients(ContainerBuilder $container, array $config)
     {
         $httpClient = $config['discovery']['client'];
-        if ($httpClient !== 'auto') {
+        if ('auto' !== $httpClient) {
             $container->removeDefinition('httplug.auto_discovery.auto_discovered_client');
             $container->removeDefinition('httplug.collector.auto_discovered_client');
 
@@ -380,7 +381,7 @@ private function configureAutoDiscoveryClients(ContainerBuilder $container, arra
         }
 
         $asyncHttpClient = $config['discovery']['async_client'];
-        if ($asyncHttpClient !== 'auto') {
+        if ('auto' !== $asyncHttpClient) {
             $container->removeDefinition('httplug.auto_discovery.auto_discovered_async');
             $container->removeDefinition('httplug.collector.auto_discovered_async');
 
diff --git a/Discovery/ConfiguredClientsStrategy.php b/Discovery/ConfiguredClientsStrategy.php
index 75f76007..cec82c4b 100644
--- a/Discovery/ConfiguredClientsStrategy.php
+++ b/Discovery/ConfiguredClientsStrategy.php
@@ -43,13 +43,13 @@ public function __construct(HttpClient $httpClient = null, HttpAsyncClient $asyn
      */
     public static function getCandidates($type)
     {
-        if ($type === HttpClient::class && self::$client !== null) {
+        if (HttpClient::class === $type && null !== self::$client) {
             return [['class' => function () {
                 return self::$client;
             }]];
         }
 
-        if ($type === HttpAsyncClient::class && self::$asyncClient !== null) {
+        if (HttpAsyncClient::class === $type && null !== self::$asyncClient) {
             return [['class' => function () {
                 return self::$asyncClient;
             }]];