Remove warnings from usage of arguments of wrong type in php 8.1

src/Api/Parser/AbstractRestParser.php

@@ -160,7 +160,7 @@ private function extractHeaders(
         // Check if the headers are prefixed by a location name
         $result[$name] = [];
         $prefix = $shape['locationName'];
-        $prefixLen = strlen($prefix);
+        $prefixLen = $prefix !== null ? strlen($prefix) : 0;
 
         foreach ($response->getHeaders() as $k => $values) {
             if (!$prefixLen) {

src/Api/Serializer/JsonBody.php

@@ -29,7 +29,7 @@ public function __construct(Service $api)
     public static function getContentType(Service $service)
     {
         return 'application/x-amz-json-'
-            . number_format($service->getMetadata('jsonVersion'), 1);
+            . number_format(($version = $service->getMetadata('jsonVersion')) !== null ? $version : 0.0, 1);
     }
 
     /**

src/Arn/ArnParser.php

@@ -23,7 +23,7 @@ class ArnParser
      */
     public static function isArn($string)
     {
-        return strpos($string, 'arn:') === 0;
+        return $string !== null && strpos($string, 'arn:') === 0;
     }
 
     /**

src/S3/S3Client.php

@@ -429,7 +429,7 @@ public function __construct(array $args)
      */
     public static function isBucketDnsCompatible($bucket)
     {
-        $bucketLen = strlen($bucket);
+        $bucketLen = $bucket !== null ? strlen($bucket) : 0;
 
         return ($bucketLen >= 3 && $bucketLen <= 63) &&
             // Cannot look like an IP address

tests/Integ/S3Context.php

@@ -411,7 +411,7 @@ private static function executeWithRetries(
                     throw $e;
                 }
                 $attempts++;
-                sleep(pow(1.2, $attempts));
+                sleep((int) pow(1.2, $attempts));
             }
         }
     }