fix default initialisation of stream (causes problems when upcasting)

bramble-core/src/main/java/org/briarproject/bramble/mailbox/protocol/MailboxRequestTake.java

@@ -5,7 +5,7 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.data.BdfList;
 
 public class MailboxRequestTake extends MailboxRequest {
-	private byte[] encryptedSyncStream = null;
+	private byte[] encryptedSyncStream;
 
 	public MailboxRequestTake(byte[] encryptedSyncStream) {
 		super(TYPE.TAKE);