src/main/java/org/intellimate/izou/sdk/events/Event.java
public Event addDescriptor(String descriptor) {
        List<String> newDescriptors = new ArrayList<>();
        newDescriptors.addAll(descriptors);
        newDescriptors.add(descriptor);
        return new Event(getType(), getSource(), newDescriptors);
    }
public Event addDescriptor(String descriptor) {
        List<String> newDescriptors = new ArrayList<>();
        newDescriptors.addAll(descriptors);
        newDescriptors.add(descriptor);
        return new Event(getType(), getSource(), newDescriptors);
    }
sets the Descriptors (but not the Event-Type).
@param descriptor a String describing the Event.
@return the resulting Event (which is the same instance)