Add some PHPDoc return types and fixes

lib/ApiRequestor.php

@@ -295,9 +295,8 @@ private static function _formatAppInfo($appInfo)
     /**
      * @static
      *
-     * @param string $disabledFunctionsOutput - String value of the 'disable_function' setting, as output by \ini_get('disable_functions')
+     * @param string $disableFunctionsOutput - String value of the 'disable_function' setting, as output by \ini_get('disable_functions')
      * @param string $functionName - Name of the function we are interesting in seeing whether or not it is disabled
-     * @param mixed $disableFunctionsOutput
      *
      * @return bool
      */
@@ -474,8 +473,7 @@ private function _requestRaw($method, $url, $params, $headers)
      * @param string $url
      * @param array $params
      * @param array $headers
-     * @param callable $readBodyChunk
-     * @param mixed $readBodyChunkCallable
+     * @param callable $readBodyChunkCallable
      *
      * @throws Exception\AuthenticationException
      * @throws Exception\ApiConnectionException

lib/Collection.php

@@ -50,6 +50,9 @@ public function setFilters($filters)
         $this->filters = $filters;
     }
 
+    /**
+     * @return mixed
+     */
     #[\ReturnTypeWillChange]
     public function offsetGet($k)
     {

lib/SearchResult.php

@@ -62,6 +62,9 @@ public function setFilters($filters)
         $this->filters = $filters;
     }
 
+    /**
+     * @return mixed
+     */
     #[\ReturnTypeWillChange]
     public function offsetGet($k)
     {

lib/StripeObject.php

@@ -149,6 +149,11 @@ public function __set($k, $v)
         $this->_unsavedValues->add($k);
     }
 
+    /**
+     * @param mixed $k
+     *
+     * @return bool
+     */
     public function __isset($k)
     {
         return isset($this->_values[$k]);
@@ -187,31 +192,48 @@ public function &__get($k)
         return $nullval;
     }
 
-    // Magic method for var_dump output. Only works with PHP >= 5.6
+    /**
+     * Magic method for var_dump output. Only works with PHP >= 5.6.
+     *
+     * @return array
+     */
     public function __debugInfo()
     {
         return $this->_values;
     }
 
     // ArrayAccess methods
+
+    /**
+     * @return void
+     */
     #[\ReturnTypeWillChange]
     public function offsetSet($k, $v)
     {
         $this->{$k} = $v;
     }
 
+    /**
+     * @return bool
+     */
     #[\ReturnTypeWillChange]
     public function offsetExists($k)
     {
         return \array_key_exists($k, $this->_values);
     }
 
+    /**
+     * @return void
+     */
     #[\ReturnTypeWillChange]
     public function offsetUnset($k)
     {
         unset($this->{$k});
     }
 
+    /**
+     * @return mixed
+     */
     #[\ReturnTypeWillChange]
     public function offsetGet($k)
     {

lib/Util/CaseInsensitiveArray.php

@@ -21,6 +21,9 @@ public function __construct($initial_array = [])
         $this->container = \array_change_key_case($initial_array, \CASE_LOWER);
     }
 
+    /**
+     * @return int
+     */
     #[\ReturnTypeWillChange]
     public function count()
     {