fix(e2ee): unknown value

Signed-off-by: alperozturk96 <alper_ozturk@proton.me>

Author: alperozturk96

library/src/main/java/com/owncloud/android/lib/resources/status/E2EVersion.kt

@@ -20,7 +20,7 @@ enum class E2EVersion(
 
     val value: String = values.last()
 
-    var unknownValue: String? = ""
+    var unknownValue: String? = null
 
     companion object {
         fun max(): E2EVersion = V2_1