diff --git a/src/Bot/Model/Response/AssignResponse.php b/src/Bot/Model/Response/AssignResponse.php
index 3f92a2d..4a766ab 100644
--- a/src/Bot/Model/Response/AssignResponse.php
+++ b/src/Bot/Model/Response/AssignResponse.php
@@ -104,7 +104,7 @@ public function getPreviousResponsible(): ?Responsible
     /**
      * @param Responsible $previousResponsible
      */
-    public function setPreviousResponsible(Responsible $previousResponsible)
+    public function setPreviousResponsible(?Responsible $previousResponsible)
     {
         $this->previousResponsible = $previousResponsible;
     }