Jackson: get a null reference on deserializing

First of all, this definetely looks like a bug in Jackson since error only appears in version 2.8.0 and later.

As to the source of the error, it appears that the reason for it is your configuration for ActivityDTO, specifically this annotation:

@JsonIgnoreProperties(value = {"parentActivity"})
private Set<ActivityDTO> subActivities;

So you have 3 options:

1. Rollback to Jackson 2.7.9
2. Make custom deserializer for this case
3. Remove this annotation and use custom serializer (if needed)