diff --git a/src/Model/Tag/CountryResponse.php b/src/Model/Tag/CountryResponse.php
index aae3b7c..22dfd0f 100644
--- a/src/Model/Tag/CountryResponse.php
+++ b/src/Model/Tag/CountryResponse.php
@@ -22,10 +22,6 @@ final class CountryResponse implements ApiResponse
      * @var array [locale => data[]]
      */
     private $countries;
-
-    /**
-     * @var string
-     */
     private $tag;
 
     private function __construct()
diff --git a/src/Model/Tag/DeleteResponse.php b/src/Model/Tag/DeleteResponse.php
index 930f51f..85211d3 100644
--- a/src/Model/Tag/DeleteResponse.php
+++ b/src/Model/Tag/DeleteResponse.php
@@ -18,31 +18,21 @@ use Mailgun\Model\ApiResponse;
  */
 final class DeleteResponse implements ApiResponse
 {
-    /**
-     * @var string
-     */
     private $message;
 
-    /**
-     * @param string $message
-     */
-    private function __construct($message)
+    private function __construct()
     {
-        $this->message = $message;
     }
 
-    /**
-     * @return DeleteResponse
-     */
-    public static function create(array $data)
+    public static function create(array $data): self
     {
-        return new self($data['message']);
+        $model = new self();
+        $model->message = $data['message'] ?? '';
+
+        return $model;
     }
 
-    /**
-     * @return string
-     */
-    public function getMessage()
+    public function getMessage(): string
     {
         return $this->message;
     }
diff --git a/src/Model/Tag/DeviceResponse.php b/src/Model/Tag/DeviceResponse.php
index 472eae8..87e7a47 100644
--- a/src/Model/Tag/DeviceResponse.php
+++ b/src/Model/Tag/DeviceResponse.php
@@ -22,10 +22,6 @@ final class DeviceResponse implements ApiResponse
      * @var array [name => data[]]
      */
     private $devices;
-
-    /**
-     * @var string
-     */
     private $tag;
 
     private function __construct()
diff --git a/src/Model/Tag/IndexResponse.php b/src/Model/Tag/IndexResponse.php
index a05b689..7eb47b6 100644
--- a/src/Model/Tag/IndexResponse.php
+++ b/src/Model/Tag/IndexResponse.php
@@ -11,9 +11,9 @@ declare(strict_types=1);
 
 namespace Mailgun\Model\Tag;
 
+use Mailgun\Model\ApiResponse;
 use Mailgun\Model\PaginationResponse;
 use Mailgun\Model\PagingProvider;
-use Mailgun\Model\ApiResponse;
 
 /**
  * @author Tobias Nyholm <tobias.nyholm@gmail.com>
@@ -27,32 +27,29 @@ final class IndexResponse implements ApiResponse, PagingProvider
      */
     private $items;
 
-    /**
-     * @param Tag[] $items
-     */
-    private function __construct(array $items, array $paging)
+    private function __construct()
     {
-        $this->items = $items;
-        $this->paging = $paging;
     }
 
-    /**
-     * @return IndexResponse
-     */
-    public static function create(array $data)
+    public static function create(array $data): self
     {
         $items = [];
         foreach ($data['items'] as $item) {
             $items[] = Tag::create($item);
         }
 
-        return new self($items, $data['paging']);
+        $model = new self();
+
+        $model->items = $items;
+        $model->paging = $data['paging'];
+
+        return $model;
     }
 
     /**
      * @return Tag[]
      */
-    public function getItems()
+    public function getItems(): array
     {
         return $this->items;
     }
diff --git a/src/Model/Tag/ProviderResponse.php b/src/Model/Tag/ProviderResponse.php
index 8427778..21ca415 100644
--- a/src/Model/Tag/ProviderResponse.php
+++ b/src/Model/Tag/ProviderResponse.php
@@ -22,10 +22,6 @@ final class ProviderResponse implements ApiResponse
      * @var array [name => data[]]
      */
     private $providers;
-
-    /**
-     * @var string
-     */
     private $tag;
 
     private function __construct()
diff --git a/src/Model/Tag/StatisticsResponse.php b/src/Model/Tag/StatisticsResponse.php
index a4f5bdb..5018f19 100644
--- a/src/Model/Tag/StatisticsResponse.php
+++ b/src/Model/Tag/StatisticsResponse.php
@@ -18,110 +18,57 @@ use Mailgun\Model\ApiResponse;
  */
 final class StatisticsResponse implements ApiResponse
 {
-    /**
-     * @var string
-     */
     private $tag;
-
-    /**
-     * @var string
-     */
     private $description;
-
-    /**
-     * @var string
-     */
     private $resolution;
-
-    /**
-     * @var \DateTime
-     */
     private $start;
-
-    /**
-     * @var \DateTime
-     */
     private $end;
-
-    /**
-     * @var array
-     */
     private $stats;
 
-    /**
-     * @param string $tag
-     * @param string $description
-     * @param string $resolution
-     */
-    private function __construct($tag, $description, \DateTime $start, \DateTime $end, $resolution, array $stats)
+    private function __construct()
     {
-        $this->tag = $tag;
-        $this->description = $description;
-        $this->resolution = $resolution;
-        $this->start = $start;
-        $this->end = $end;
-        $this->stats = $stats;
     }
 
-    /**
-     * @return StatisticsResponse
-     */
-    public static function create(array $data)
+    public static function create(array $data): self
     {
-        return new self(
-            $data['tag'],
-            $data['description'],
-            new \DateTime($data['start']),
-            new \DateTime($data['end']),
-            $data['resolution'],
-            $data['stats']
-        );
+        $model = new self();
+
+        $model->tag = $data['tag'] ?? '';
+        $model->description = $data['description'] ?? '';
+        $model->resolution = $data['resolution'] ?? null;
+        $model->stats = $data['stats'] ?? [];
+        $model->start = isset($data['start']) ? new \DateTimeImmutable($data['start']) : null;
+        $model->end = isset($data['end']) ? new \DateTimeImmutable($data['end']) : null;
+
+        return $model;
     }
 
-    /**
-     * @return string
-     */
-    public function getTag()
+    public function getTag(): string
     {
         return $this->tag;
     }
 
-    /**
-     * @return string
-     */
-    public function getDescription()
+    public function getDescription(): string
     {
         return $this->description;
     }
 
-    /**
-     * @return string
-     */
-    public function getResolution()
+    public function getResolution(): ?string
     {
         return $this->resolution;
     }
 
-    /**
-     * @return \DateTime
-     */
-    public function getStart()
+    public function getStart(): ?\DateTimeImmutable
     {
         return $this->start;
     }
 
-    /**
-     * @return \DateTime
-     */
-    public function getEnd()
+    public function getEnd(): ?\DateTimeImmutable
     {
         return $this->end;
     }
 
-    /**
-     * @return array
-     */
-    public function getStats()
+    public function getStats(): array
     {
         return $this->stats;
     }
diff --git a/src/Model/Tag/Tag.php b/src/Model/Tag/Tag.php
index 6357775..e5b41d5 100644
--- a/src/Model/Tag/Tag.php
+++ b/src/Model/Tag/Tag.php
@@ -13,79 +13,43 @@ namespace Mailgun\Model\Tag;
 
 class Tag
 {
-    /**
-     * @var string
-     */
     private $tag;
-
-    /**
-     * @var string
-     */
     private $description;
-
-    /**
-     * @var \DateTime
-     */
     private $firstSeen;
-
-    /**
-     * @var \DateTime
-     */
     private $lastSeen;
 
-    /**
-     * @param string    $tag
-     * @param string    $description
-     * @param \DateTime $firstSeen
-     * @param \DateTime $lastSeen
-     */
-    private function __construct($tag, $description, \DateTime $firstSeen = null, \DateTime $lastSeen = null)
+    private function __construct()
     {
-        $this->tag = $tag;
-        $this->description = $description;
-        $this->firstSeen = $firstSeen;
-        $this->lastSeen = $lastSeen;
     }
 
-    /**
-     * @return Tag
-     */
-    public static function create(array $data)
+    public static function create(array $data): self
     {
-        $firstSeen = isset($data['first-seen']) ? new \DateTime($data['first-seen']) : null;
-        $lastSeen = isset($data['last-seen']) ? new \DateTime($data['last-seen']) : null;
+        $model = new self();
 
-        return new self($data['tag'], $data['description'], $firstSeen, $lastSeen);
+        $model->tag = $data['tag'] ?? '';
+        $model->description = $data['description'] ?? '';
+        $model->firstSeen = isset($data['first-seen']) ? new \DateTimeImmutable($data['first-seen']) : null;
+        $model->lastSeen = isset($data['last-seen']) ? new \DateTimeImmutable($data['last-seen']) : null;
+
+        return $model;
     }
 
-    /**
-     * @return string
-     */
-    public function getTag()
+    public function getTag(): string
     {
         return $this->tag;
     }
 
-    /**
-     * @return string
-     */
-    public function getDescription()
+    public function getDescription(): string
     {
         return $this->description;
     }
 
-    /**
-     * @return \DateTime
-     */
-    public function getFirstSeen()
+    public function getFirstSeen(): ?\DateTimeImmutable
     {
         return $this->firstSeen;
     }
 
-    /**
-     * @return \DateTime
-     */
-    public function getLastSeen()
+    public function getLastSeen(): ?\DateTimeImmutable
     {
         return $this->lastSeen;
     }
diff --git a/src/Model/Tag/UpdateResponse.php b/src/Model/Tag/UpdateResponse.php
index 0772705..4a9447d 100644
--- a/src/Model/Tag/UpdateResponse.php
+++ b/src/Model/Tag/UpdateResponse.php
@@ -18,31 +18,20 @@ use Mailgun\Model\ApiResponse;
  */
 final class UpdateResponse implements ApiResponse
 {
-    /**
-     * @var string
-     */
     private $message;
 
-    /**
-     * @param string $message
-     */
-    private function __construct($message)
+    private function __construct()
     {
-        $this->message = $message;
     }
 
-    /**
-     * @return UpdateResponse
-     */
-    public static function create(array $data)
+    public static function create(array $data): self
     {
-        return new self($data['message']);
+        $model = new self();
+
+        $model->message = $data['message'] ?? '';
     }
 
-    /**
-     * @return string
-     */
-    public function getMessage()
+    public function getMessage(): string
     {
         return $this->message;
     }