Fix issues in Doctrine entities newly found by PHPStan

[MAILPOET-3029]

lib/Entities/NewsletterEntity.php

@@ -97,7 +97,7 @@ class NewsletterEntity {
   private $preheader = '';
 
   /**
-   * @ORM\Column(type="json")
+   * @ORM\Column(type="json", nullable=true)
    * @var array|null
    */
   private $body;

lib/Entities/NewsletterTemplateEntity.php

@@ -39,7 +39,7 @@ class NewsletterTemplateEntity {
   private $categories = '[]';
 
   /**
-   * @ORM\Column(type="json")
+   * @ORM\Column(type="json", nullable=true)
    * @Assert\NotBlank()
    * @var array|null
    */

lib/Entities/ScheduledTaskEntity.php

@@ -58,7 +58,7 @@ class ScheduledTaskEntity {
   private $processedAt;
 
   /**
-   * @ORM\Column(type="json")
+   * @ORM\Column(type="json", nullable=true)
    * @var array|null
    */
   private $meta;

lib/Entities/SendingQueueEntity.php

@@ -72,7 +72,7 @@ class SendingQueueEntity {
   private $countToProcess = 0;
 
   /**
-   * @ORM\Column(type="json")
+   * @ORM\Column(type="json", nullable=true)
    * @var array|null
    */
   private $meta;

lib/Entities/SubscriberEntity.php

@@ -30,7 +30,7 @@ class SubscriberEntity {
 
   /**
    * @ORM\Column(type="bigint", nullable=true)
-   * @var int|null
+   * @var string|null
    */
   private $wpUserId;
 
@@ -133,14 +133,14 @@ class SubscriberEntity {
    * @return int|null
    */
   public function getWpUserId() {
-    return $this->wpUserId;
+    return $this->wpUserId ? (int)$this->wpUserId : null;
   }
 
   /**
    * @param int|null $wpUserId
    */
   public function setWpUserId($wpUserId) {
-    $this->wpUserId = $wpUserId;
+    $this->wpUserId = $wpUserId ? (string)$wpUserId : null;
   }
 
   /**