Fix a bug when saving null instead of a string

Author: johnkrovitch

composer.json

@@ -45,7 +45,8 @@
             "Sidus\\EncryptionBundle\\": "src/"
         },
         "exclude-from-classmap": [
-            "/Tests/"
+            "/Tests/",
+            "/tests/"
         ]
     },
     "autoload-dev": {

src/Doctrine/Type/Behavior/EncryptType.php

@@ -11,6 +11,9 @@ trait EncryptType
 
     public function convertToPHPValue($value, AbstractPlatform $platform): string
     {
+        if ($value === null) {
+            $value = '';
+        }
         // Decode value previously encoded in base64 for database storage
         $value = base64_decode($value);
 
@@ -19,6 +22,9 @@ public function convertToPHPValue($value, AbstractPlatform $platform): string
 
     public function convertToDatabaseValue($value, AbstractPlatform $platform): string
     {
+        if ($value === null) {
+            $value = '';
+        }
         $value = $this->valueEncrypter->encrypt($value);
 
         // Encoding to base64 to avoid issue when storing binary strings