Fix implicit nullable type issues

Author: glaubinix

lib/Bitbucket/API/Api.php

@@ -49,7 +49,7 @@ class Api
      * @param OptionalClientOption $options
      * @param ClientInterface $client
      */
-    public function __construct(array $options = array(), ClientInterface $client = null)
+    public function __construct(array $options = array(), ?ClientInterface $client = null)
     {
         $this->httpClient = (null !== $client) ? $client : new Client($options, null);
 

lib/Bitbucket/API/Http/Client.php

@@ -51,7 +51,7 @@ class Client implements ClientInterface
     /**
      * @param OptionalClientOption $options
      */
-    public function __construct(array $options = array(), HttpPluginClientBuilder $httpClientBuilder = null)
+    public function __construct(array $options = array(), ?HttpPluginClientBuilder $httpClientBuilder = null)
     {
         $this->responseHistory = new HistoryPlugin();
         $this->options = array_merge(array_merge($this->options, $options));

lib/Bitbucket/API/Http/HttpPluginClientBuilder.php

@@ -30,7 +30,7 @@ class HttpPluginClientBuilder
     /**
      * @param MessageFactory|RequestFactoryInterface|null $requestFactory
      */
-    public function __construct(ClientInterface $httpClient = null, $requestFactory = null, StreamFactoryInterface $streamFactory = null)
+    public function __construct(?ClientInterface $httpClient = null, $requestFactory = null, StreamFactoryInterface $streamFactory = null)
     {
         $requestFactory = $requestFactory ?? Psr17FactoryDiscovery::findRequestFactory();
         if ($requestFactory instanceof MessageFactory) {

lib/Bitbucket/API/Http/Response/Pager.php

@@ -38,7 +38,7 @@ public function __construct(
         HttpPluginClientBuilder $httpPluginClientBuilder,
         ResponseInterface $response,
         $messageFactory = null,
-        StreamFactoryInterface $streamFactory = null
+        ?StreamFactoryInterface $streamFactory = null
     ) {
         /** @var ResponseInterface $response */
         if ($response->getStatusCode() >= 400) {