Add an instance to a service and add a milestone to an operation on the instance. Then try to update the milestone - an error is thrown to the user.
The following can be seen in the logs:

Failed to update Interface Operation with an error java.lang.NullPointerException: null\n\tat org.openecomp.sdc.be.components.impl.ComponentInterfaceOperationBusinessLogic.lambda$updateComponentInstanceInterfaceOperation$0(ComponentInterfaceOperationBusinessLogic.java:143)