Straight forward but maddening, I get this error on my RPC call: 

An IncompatibleRemoteServiceException was thrown while processing this call.
 com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException: Invalid type signature for com.milkrun.core.dto.UserBasket

Here is the class causing the issue:

```
public class UserBasket implements Serializable{

     private static final long serialVersionUID = -6761554796753637352L;

    public int userBasketID;
    public String description;
    public String userID;

    public List<BasketItem> items;

    public String createUserId;
    public Timestamp createTs;
     public String lastUpdateUserId;
    public Timestamp lastUpdateTs;
    public Timestamp effStartTs;
    public Timestamp effStopTs;

}

```

And the type BasketItem:

```
public class BasketItem implements Serializable {

private static final long serialVersionUID = -17764683871112216L;

public int basketItemID;

public String upc;
public String description;
public String brandName;

public BigDecimal price;

public String createUserId;
public Timestamp createTs;
public String lastUpdateUserId;
public Timestamp lastUpdateTs;
public Timestamp effStartTs;
public Timestamp effStopTs;

}

```

I'm not sure where I'm going wrong and I'd rather not use IsSerializable as these DTOs are in a project shared by an android app too and IsSerializable is part of the GWT stack.