adding php81 compatibility

README.md

@@ -7,7 +7,7 @@ The Trolley PHP SDK provides integration access to the Trolley API.
 
 ## Requirements
 
-PHP version >= 5.4.0 is required.
+PHP version >= 8.1 is required.
 
 The following PHP extensions are required:
 

composer.json

@@ -15,15 +15,15 @@
         }
     ],
     "require": {
-        "php": ">=5.4",
+        "php": ">=8.1",
         "ext-curl": "*",
         "ext-json": "*",
         "ext-mbstring": "*",
         "ext-openssl": "*",
         "vlucas/phpdotenv": "^5.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "5.7.*",
+        "phpunit/phpunit": "9.*",
         "ramsey/uuid": "*"
     },
     "autoload": {

lib/Trolley/ResourceCollection.php

@@ -56,19 +56,19 @@ public function  __construct($response, $items, $pager)
     /**
      * returns the current item when iterating with foreach
      */
-    public function current()
+    public function current(): mixed
     {
-        return $this->_items[$this->_index];
+        return $this->_items[$this->_index] ?? false;
     }
 
     /**
      * returns the first item in the collection
      *
      * @return mixed
      */
-    public function firstItem()
+    public function firstItem(): mixed
     {
-        return $this->_items[0];
+        return $this->_items[0] ?? false;
     }
 
     public function key()
@@ -79,23 +79,23 @@ public function key()
     /**
      * advances to the next item in the collection when iterating with foreach
      */
-    public function next()
+    public function next(): void
     {
         ++$this->_index;
     }
 
     /**
      * rewinds the testIterateOverResults collection to the first item when iterating with foreach
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->_index = 0;
     }
 
     /**
      * returns whether the current item is valid when iterating with foreach
      */
-    public function valid()
+    public function valid(): bool
     {
         if ($this->_index >= count($this->_items)) {
             if ($this->_page + 1 >= $this->_maxPages) {
@@ -111,20 +111,22 @@ public function maximumCount()
         return $this->_records;
     }
 
-    private function _getNextPage()
+    private function _getNextPage(): void
     {
         $result = $this->_getPage($this->_page + 1);
         $this->_items = $result->_items;
         $this->_index = 0;
         ++$this->_page;
     }
 
-    /**
-     * requests the next page of results for the collection
-     *
-     * @return void
-     */
-    private function _getPage($page)
+	/**
+	 * requests the next page of results for the collection
+	 *
+	 * @param $page
+	 *
+	 * @return mixed
+	 */
+    private function _getPage($page): mixed
     {
         $object = $this->_pager['object'];
         $method = $this->_pager['method'];