UMCS-655 Fix serialization causes StackOverflow errors (#89)

Author: GreatG0ose

CHANGELOG.md

@@ -19,6 +19,7 @@ This release adds Klarna payment type to Java SDK.
 ### Fixed
 
 * Fixed typo `ShippingAddress.Type:DIFFERENT_ADDRESSES` -> `ShippingAddress.Type:DIFFERENT_ADDRESS`. This typo caused errors on authorize/charge in some payment cases
+* Fixed (de-)serialization of `AbstractTransaction` cause infinite Webhook calls.
 
 ## [1.2.1.0][1.2.1.0]
 

src/main/java/com/unzer/payment/AbstractTransaction.java

@@ -25,7 +25,6 @@
 import java.util.Date;
 
 public abstract class AbstractTransaction<T extends AbstractPayment> implements PaymentType {
-
     private String id;
     private BigDecimal amount;
     private Currency currency;
@@ -48,9 +47,9 @@ public abstract class AbstractTransaction<T extends AbstractPayment> implements
     private String type;
     private AdditionalTransactionData additionalTransactionData;
     @JsonFieldIgnore
-    private T payment;
+    private transient T payment;
     @JsonFieldIgnore
-    private Unzer unzer;
+    private transient Unzer unzer;
     @JsonFieldIgnore
     private URL resourceUrl;