diff --git a/src/BatchClient.php b/src/BatchClient.php
index 09a83ff..ad65177 100644
--- a/src/BatchClient.php
+++ b/src/BatchClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception;
diff --git a/src/BatchClientInterface.php b/src/BatchClientInterface.php
index ce6c3c7..56a34ae 100644
--- a/src/BatchClientInterface.php
+++ b/src/BatchClientInterface.php
@@ -1,8 +1,9 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
-use Http\Client\Exception;
 use Http\Client\HttpClient;
 use Http\Client\Common\Exception\BatchException;
 use Psr\Http\Message\RequestInterface;
diff --git a/src/BatchResult.php b/src/BatchResult.php
index 94ff51a..4202c70 100644
--- a/src/BatchResult.php
+++ b/src/BatchResult.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception;
diff --git a/src/Deferred.php b/src/Deferred.php
index c294a8d..7c3f9f5 100644
--- a/src/Deferred.php
+++ b/src/Deferred.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception;
diff --git a/src/EmulatedHttpAsyncClient.php b/src/EmulatedHttpAsyncClient.php
index 9d6c557..f88e27d 100644
--- a/src/EmulatedHttpAsyncClient.php
+++ b/src/EmulatedHttpAsyncClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/EmulatedHttpClient.php b/src/EmulatedHttpClient.php
index d99b4e4..5c2d8c4 100644
--- a/src/EmulatedHttpClient.php
+++ b/src/EmulatedHttpClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/Exception/BatchException.php b/src/Exception/BatchException.php
index 8620f9d..5167842 100644
--- a/src/Exception/BatchException.php
+++ b/src/Exception/BatchException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\TransferException;
diff --git a/src/Exception/CircularRedirectionException.php b/src/Exception/CircularRedirectionException.php
index 73ec521..de2063e 100644
--- a/src/Exception/CircularRedirectionException.php
+++ b/src/Exception/CircularRedirectionException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\HttpException;
diff --git a/src/Exception/ClientErrorException.php b/src/Exception/ClientErrorException.php
index b1f6cc8..1b187e7 100644
--- a/src/Exception/ClientErrorException.php
+++ b/src/Exception/ClientErrorException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\HttpException;
diff --git a/src/Exception/HttpClientNotFoundException.php b/src/Exception/HttpClientNotFoundException.php
index 5d33f98..5f16053 100644
--- a/src/Exception/HttpClientNotFoundException.php
+++ b/src/Exception/HttpClientNotFoundException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\TransferException;
diff --git a/src/Exception/LoopException.php b/src/Exception/LoopException.php
index e834124..e84053c 100644
--- a/src/Exception/LoopException.php
+++ b/src/Exception/LoopException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\RequestException;
diff --git a/src/Exception/MultipleRedirectionException.php b/src/Exception/MultipleRedirectionException.php
index ae514cd..4c7814e 100644
--- a/src/Exception/MultipleRedirectionException.php
+++ b/src/Exception/MultipleRedirectionException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\HttpException;
diff --git a/src/Exception/ServerErrorException.php b/src/Exception/ServerErrorException.php
index 665d724..1ad2552 100644
--- a/src/Exception/ServerErrorException.php
+++ b/src/Exception/ServerErrorException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Exception;
 
 use Http\Client\Exception\HttpException;
diff --git a/src/FlexibleHttpClient.php b/src/FlexibleHttpClient.php
index 58f8813..da42734 100644
--- a/src/FlexibleHttpClient.php
+++ b/src/FlexibleHttpClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/HttpAsyncClientDecorator.php b/src/HttpAsyncClientDecorator.php
index 6eb576c..2714b4a 100644
--- a/src/HttpAsyncClientDecorator.php
+++ b/src/HttpAsyncClientDecorator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/HttpAsyncClientEmulator.php b/src/HttpAsyncClientEmulator.php
index ce16f84..53c2535 100644
--- a/src/HttpAsyncClientEmulator.php
+++ b/src/HttpAsyncClientEmulator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception;
diff --git a/src/HttpClientDecorator.php b/src/HttpClientDecorator.php
index da5a1bb..37c87e6 100644
--- a/src/HttpClientDecorator.php
+++ b/src/HttpClientDecorator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpClient;
diff --git a/src/HttpClientEmulator.php b/src/HttpClientEmulator.php
index 8e6472a..51e2c05 100644
--- a/src/HttpClientEmulator.php
+++ b/src/HttpClientEmulator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Psr\Http\Message\RequestInterface;
diff --git a/src/HttpClientPool.php b/src/HttpClientPool.php
index a730f50..a1b8dcb 100644
--- a/src/HttpClientPool.php
+++ b/src/HttpClientPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Common\HttpClientPool\HttpClientPoolItem;
diff --git a/src/HttpClientPool/HttpClientPool.php b/src/HttpClientPool/HttpClientPool.php
index cbac805..f92f185 100644
--- a/src/HttpClientPool/HttpClientPool.php
+++ b/src/HttpClientPool/HttpClientPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\HttpClientPool;
 
 use Http\Client\Common\Exception\HttpClientNotFoundException;
diff --git a/src/HttpClientPool/HttpClientPoolItem.php b/src/HttpClientPool/HttpClientPoolItem.php
index 4094502..ce121de 100644
--- a/src/HttpClientPool/HttpClientPoolItem.php
+++ b/src/HttpClientPool/HttpClientPoolItem.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\HttpClientPool;
 
 use Http\Client\Common\FlexibleHttpClient;
diff --git a/src/HttpClientPool/LeastUsedClientPool.php b/src/HttpClientPool/LeastUsedClientPool.php
index e3c29b7..789c357 100644
--- a/src/HttpClientPool/LeastUsedClientPool.php
+++ b/src/HttpClientPool/LeastUsedClientPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\HttpClientPool;
 
 use Http\Client\Common\Exception\HttpClientNotFoundException;
diff --git a/src/HttpClientPool/RandomClientPool.php b/src/HttpClientPool/RandomClientPool.php
index 3adf5fd..789ba42 100644
--- a/src/HttpClientPool/RandomClientPool.php
+++ b/src/HttpClientPool/RandomClientPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\HttpClientPool;
 
 use Http\Client\Common\Exception\HttpClientNotFoundException;
diff --git a/src/HttpClientPool/RoundRobinClientPool.php b/src/HttpClientPool/RoundRobinClientPool.php
index 13cdf13..7c7b191 100644
--- a/src/HttpClientPool/RoundRobinClientPool.php
+++ b/src/HttpClientPool/RoundRobinClientPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\HttpClientPool;
 
 use Http\Client\Common\Exception\HttpClientNotFoundException;
diff --git a/src/HttpClientRouter.php b/src/HttpClientRouter.php
index 56be0bf..05ad051 100644
--- a/src/HttpClientRouter.php
+++ b/src/HttpClientRouter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception\RequestException;
diff --git a/src/HttpClientRouterInterface.php b/src/HttpClientRouterInterface.php
index 67fb822..6e490f3 100644
--- a/src/HttpClientRouterInterface.php
+++ b/src/HttpClientRouterInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/HttpMethodsClient.php b/src/HttpMethodsClient.php
index 69e4df9..bcc14b3 100644
--- a/src/HttpMethodsClient.php
+++ b/src/HttpMethodsClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpClient;
diff --git a/src/HttpMethodsClientInterface.php b/src/HttpMethodsClientInterface.php
index 6bc409f..20fbf03 100644
--- a/src/HttpMethodsClientInterface.php
+++ b/src/HttpMethodsClientInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Exception;
diff --git a/src/Plugin.php b/src/Plugin.php
index ab7e4a1..cbc9592 100644
--- a/src/Plugin.php
+++ b/src/Plugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Promise\Promise;
diff --git a/src/Plugin/AddHostPlugin.php b/src/Plugin/AddHostPlugin.php
index 492667e..db89d34 100644
--- a/src/Plugin/AddHostPlugin.php
+++ b/src/Plugin/AddHostPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/AddPathPlugin.php b/src/Plugin/AddPathPlugin.php
index 0a2adba..5b0b01a 100644
--- a/src/Plugin/AddPathPlugin.php
+++ b/src/Plugin/AddPathPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/AuthenticationPlugin.php b/src/Plugin/AuthenticationPlugin.php
index 5b6c447..ce9d4bd 100644
--- a/src/Plugin/AuthenticationPlugin.php
+++ b/src/Plugin/AuthenticationPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/BaseUriPlugin.php b/src/Plugin/BaseUriPlugin.php
index ee9e075..825709b 100644
--- a/src/Plugin/BaseUriPlugin.php
+++ b/src/Plugin/BaseUriPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/ContentLengthPlugin.php b/src/Plugin/ContentLengthPlugin.php
index dff2ca8..f313c33 100644
--- a/src/Plugin/ContentLengthPlugin.php
+++ b/src/Plugin/ContentLengthPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/ContentTypePlugin.php b/src/Plugin/ContentTypePlugin.php
index 190f125..f6dcddd 100644
--- a/src/Plugin/ContentTypePlugin.php
+++ b/src/Plugin/ContentTypePlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/CookiePlugin.php b/src/Plugin/CookiePlugin.php
index 84669cf..8f8d5b0 100644
--- a/src/Plugin/CookiePlugin.php
+++ b/src/Plugin/CookiePlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
@@ -127,7 +129,7 @@ private function createCookie(RequestInterface $request, $setCookie)
                                 $name,
                                 $value
                             ),
-                            null,
+                            0,
                             $e
                         );
                     }
diff --git a/src/Plugin/DecoderPlugin.php b/src/Plugin/DecoderPlugin.php
index 0930779..b1ede5d 100644
--- a/src/Plugin/DecoderPlugin.php
+++ b/src/Plugin/DecoderPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/ErrorPlugin.php b/src/Plugin/ErrorPlugin.php
index 1d25fb7..2d1d2f1 100644
--- a/src/Plugin/ErrorPlugin.php
+++ b/src/Plugin/ErrorPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Exception\ClientErrorException;
diff --git a/src/Plugin/HeaderAppendPlugin.php b/src/Plugin/HeaderAppendPlugin.php
index ca44836..95ea673 100644
--- a/src/Plugin/HeaderAppendPlugin.php
+++ b/src/Plugin/HeaderAppendPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/HeaderDefaultsPlugin.php b/src/Plugin/HeaderDefaultsPlugin.php
index 77ffe8c..bf58070 100644
--- a/src/Plugin/HeaderDefaultsPlugin.php
+++ b/src/Plugin/HeaderDefaultsPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/HeaderRemovePlugin.php b/src/Plugin/HeaderRemovePlugin.php
index 0a34248..9f4ca44 100644
--- a/src/Plugin/HeaderRemovePlugin.php
+++ b/src/Plugin/HeaderRemovePlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/HeaderSetPlugin.php b/src/Plugin/HeaderSetPlugin.php
index 210bb42..06f00eb 100644
--- a/src/Plugin/HeaderSetPlugin.php
+++ b/src/Plugin/HeaderSetPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/HistoryPlugin.php b/src/Plugin/HistoryPlugin.php
index 7b14485..a147d2e 100644
--- a/src/Plugin/HistoryPlugin.php
+++ b/src/Plugin/HistoryPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/Journal.php b/src/Plugin/Journal.php
index 15f3095..46f0a7b 100644
--- a/src/Plugin/Journal.php
+++ b/src/Plugin/Journal.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Exception;
diff --git a/src/Plugin/QueryDefaultsPlugin.php b/src/Plugin/QueryDefaultsPlugin.php
index 2693507..4c8087c 100644
--- a/src/Plugin/QueryDefaultsPlugin.php
+++ b/src/Plugin/QueryDefaultsPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/RedirectPlugin.php b/src/Plugin/RedirectPlugin.php
index 89b0f39..e562553 100644
--- a/src/Plugin/RedirectPlugin.php
+++ b/src/Plugin/RedirectPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Exception\CircularRedirectionException;
diff --git a/src/Plugin/RequestMatcherPlugin.php b/src/Plugin/RequestMatcherPlugin.php
index d7d3f3d..fdf9377 100644
--- a/src/Plugin/RequestMatcherPlugin.php
+++ b/src/Plugin/RequestMatcherPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/RetryPlugin.php b/src/Plugin/RetryPlugin.php
index a0da75c..42b3981 100644
--- a/src/Plugin/RetryPlugin.php
+++ b/src/Plugin/RetryPlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Http\Client\Common\Plugin;
diff --git a/src/Plugin/VersionBridgePlugin.php b/src/Plugin/VersionBridgePlugin.php
index f3891e5..45c4364 100644
--- a/src/Plugin/VersionBridgePlugin.php
+++ b/src/Plugin/VersionBridgePlugin.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common\Plugin;
 
 use Psr\Http\Message\RequestInterface;
diff --git a/src/PluginClient.php b/src/PluginClient.php
index 264c2fe..fca30a7 100644
--- a/src/PluginClient.php
+++ b/src/PluginClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\Common\Exception\LoopException;
diff --git a/src/PluginClientFactory.php b/src/PluginClientFactory.php
index 77642ea..cb07a89 100644
--- a/src/PluginClientFactory.php
+++ b/src/PluginClientFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Http\Client\HttpAsyncClient;
diff --git a/src/VersionBridgeClient.php b/src/VersionBridgeClient.php
index 048eeae..f8ab773 100644
--- a/src/VersionBridgeClient.php
+++ b/src/VersionBridgeClient.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Http\Client\Common;
 
 use Psr\Http\Message\RequestInterface;