Fix JWE serialiser crashing on decoding invalid JWE (#186)

The JWE serialiser crashes when attempting to decode invalid data or even a JWS. The serialiser returns null but checkData does not accept a null value and throws an exception.

Author: mdeboer

src/Component/Encryption/Serializer/JSONFlattenedSerializer.php

@@ -88,9 +88,9 @@ public function unserialize(string $input): JWE
         );
     }
 
-    private function checkData(array $data): void
+    private function checkData(?array $data): void
     {
-        if (!isset($data['ciphertext']) || isset($data['recipients'])) {
+        if ($data === null || !isset($data['ciphertext']) || isset($data['recipients'])) {
             throw new InvalidArgumentException('Unsupported input.');
         }
     }

src/Component/Encryption/Serializer/JSONGeneralSerializer.php

@@ -97,9 +97,9 @@ public function unserialize(string $input): JWE
         );
     }
 
-    private function checkData(array $data): void
+    private function checkData(?array $data): void
     {
-        if (!isset($data['ciphertext']) || !isset($data['recipients'])) {
+        if ($data === null || !isset($data['ciphertext']) || !isset($data['recipients'])) {
             throw new InvalidArgumentException('Unsupported input.');
         }
     }