diff --git a/src/Encryption/EntityEncryption.php b/src/Encryption/EntityEncryption.php
index db76ddb..a1b5cf7 100644
--- a/src/Encryption/EntityEncryption.php
+++ b/src/Encryption/EntityEncryption.php
@@ -163,9 +163,13 @@ protected function process(object $entity) : array
         return $marked;
     }
 
-    protected function hasMarker(string $value) : bool
+    protected function hasMarker(?string $value) : bool
     {
-        $substr = strpos($value, self::ENCRYPTION_MARKER);
+        $substr = false;
+
+        if ($value !== null) {
+            $substr = strpos($value, self::ENCRYPTION_MARKER);
+        }
 
         return $substr !== false;
     }