Do not use DateTimeImmutable.

Entity/AccompanyingPeriod.php

@@ -25,7 +25,6 @@ namespace Chill\PersonBundle\Entity;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
 use Chill\MainBundle\Entity\User;
-use DateTimeImmutable;
 
 /**
  * AccompanyingPeriod
@@ -35,9 +34,11 @@ class AccompanyingPeriod
     /** @var integer */
     private $id;
 
-    private DateTimeImmutable $openingDate;
+    /** @var \DateTime */
+    private $openingDate;
 
-    private ?DateTimeImmutable $closingDate = null;
+    /** @var \DateTime */
+    private $closingDate;
 
     /** @var string */
     private $remark = '';
@@ -56,11 +57,11 @@ class AccompanyingPeriod
     private $user;
 
     /**
-     *
-     * @param \DateTimeImmutable $dateOpening
+     * 
+     * @param \DateTime $dateOpening
      * @uses AccompanyingPeriod::setClosingDate()
      */
-    public function __construct(\DateTimeImmutable $dateOpening) {
+    public function __construct(\DateTime $dateOpening) {
         $this->setOpeningDate($dateOpening);
     }
 
@@ -74,14 +75,25 @@ class AccompanyingPeriod
         return $this->id;
     }
 
-    public function setOpeningDate(DateTimeImmutable $openingDate): self
+    /**
+     * Set openingDate
+     *
+     * @param \DateTime $dateOpening
+     * @return AccompanyingPeriod
+     */
+    public function setOpeningDate($openingDate)
     {
         $this->openingDate = $openingDate;
 
         return $this;
     }
 
-    public function getOpeningDate(): DateTimeImmutable
+    /**
+     * Get openingDate
+     *
+     * @return \DateTime 
+     */
+    public function getOpeningDate()
     {
         return $this->openingDate;
     }
@@ -91,14 +103,19 @@ class AccompanyingPeriod
      *
      * For closing a Person file, you should use Person::setClosed instead.
      */
-    public function setClosingDate(DateTimeImmutable $closingDate): self
+    public function setClosingDate($closingDate)
     {
         $this->closingDate = $closingDate;
 
         return $this;
     }
 
-    public function getClosingDate(): ?DateTimeImmutable
+    /**
+     * Get closingDate
+     *
+     * @return \DateTime 
+     */
+    public function getClosingDate()
     {
         return $this->closingDate;
     }
@@ -109,7 +126,7 @@ class AccompanyingPeriod
      */
     public function isOpen(): bool
     {
-        if ($this->getOpeningDate() > new \DateTimeImmutable('now')) {
+        if ($this->getOpeningDate() > new \DateTime('now')) {
             return false;
         }