diff --git a/lib/Auth/AWS.php b/lib/Auth/AWS.php
index e816f73..1e985e8 100644
--- a/lib/Auth/AWS.php
+++ b/lib/Auth/AWS.php
@@ -55,7 +55,7 @@ public function init(): bool
     {
         $authHeader = $this->request->getHeader('Authorization');
 
-        if (is_null($authHeader)) {
+        if ($authHeader === null) {
             $this->errorCode = self::ERR_NOAWSHEADER;
 
             return false;
diff --git a/lib/Client.php b/lib/Client.php
index 16b2c7c..ebc86dd 100644
--- a/lib/Client.php
+++ b/lib/Client.php
@@ -196,7 +196,7 @@ public function poll(): bool
             );
 
             if ($status && CURLMSG_DONE === $status['msg']) {
-                $resourceId = intval($status['handle']);
+                $resourceId = (int)$status['handle'];
                 list(
                     $request,
                     $successCallback,
@@ -461,7 +461,7 @@ protected function parseCurlResult(string $response, $curlHandle): array
 
         $response->setBody($responseBody);
 
-        $httpCode = intval($response->getStatus());
+        $httpCode = (int)$response->getStatus();
 
         return [
             'status' => $httpCode >= 400 ? self::STATUS_HTTPERROR : self::STATUS_SUCCESS,
@@ -487,7 +487,7 @@ protected function sendAsyncInternal(RequestInterface $request, callable $succes
             $this->createCurlSettingsArray($request)
         );
         curl_multi_add_handle($this->curlMultiHandle, $curl);
-        $this->curlMultiMap[intval($curl)] = [
+        $this->curlMultiMap[(int)$curl] = [
             $request,
             $success,
             $error,
diff --git a/lib/Message.php b/lib/Message.php
index 4972310..dff242c 100644
--- a/lib/Message.php
+++ b/lib/Message.php
@@ -52,7 +52,7 @@ public function getBodyAsStream()
         if (is_callable($this->body)) {
             $body = $this->getBodyAsString();
         }
-        if (is_string($body) || is_null($body)) {
+        if (is_string($body) || $body === null) {
             $stream = fopen('php://temp', 'r+');
             fwrite($stream, (string) $body);
             rewind($stream);
@@ -75,7 +75,7 @@ public function getBodyAsString(): string
         if (is_string($body)) {
             return $body;
         }
-        if (is_null($body)) {
+        if ($body === null) {
             return '';
         }
         if (is_callable($body)) {
@@ -220,7 +220,7 @@ public function setHeaders(array $headers)
      * another value. Individual values can be retrieved with
      * getHeadersAsArray.
      *
-     * @param scalar $value
+     * @param string|string[] $value
      */
     public function addHeader(string $name, $value)
     {
diff --git a/lib/Response.php b/lib/Response.php
index 024f211..d7bf2c2 100644
--- a/lib/Response.php
+++ b/lib/Response.php
@@ -105,13 +105,13 @@ class Response extends Message implements ResponseInterface
      */
     public function __construct($status = 500, array $headers = null, $body = null)
     {
-        if (!is_null($status)) {
+        if ($status !== null) {
             $this->setStatus($status);
         }
-        if (!is_null($headers)) {
+        if ($headers !== null) {
             $this->setHeaders($headers);
         }
-        if (!is_null($body)) {
+        if ($body !== null) {
             $this->setBody($body);
         }
     }
diff --git a/lib/Sapi.php b/lib/Sapi.php
index 7859134..bf3daae 100644
--- a/lib/Sapi.php
+++ b/lib/Sapi.php
@@ -75,7 +75,7 @@ public static function sendResponse(ResponseInterface $response)
         }
 
         $body = $response->getBody();
-        if (is_null($body)) {
+        if ($body === null) {
             return;
         }
 
@@ -199,11 +199,11 @@ public static function createFromServerArray(array $serverArray): Request
             }
         }
 
-        if (is_null($url)) {
+        if ($url === null) {
             throw new InvalidArgumentException('The _SERVER array must have a REQUEST_URI key');
         }
 
-        if (is_null($method)) {
+        if ($method === null) {
             throw new InvalidArgumentException('The _SERVER array must have a REQUEST_METHOD key');
         }
         $r = new Request($method, $url, $headers);
diff --git a/lib/functions.php b/lib/functions.php
index 373d19e..161d261 100644
--- a/lib/functions.php
+++ b/lib/functions.php
@@ -138,7 +138,7 @@ function negotiateContentType($acceptHeaderValue, array $availableOptions)
 
     foreach ($proposals as $proposal) {
         // Ignoring broken values.
-        if (is_null($proposal)) {
+        if ($proposal === null) {
             continue;
         }