For a Call-type Event, the ‘Called operation’ field must be defined, whereas the ‘Instanciated signal’ must be empty.
An Event is the specification of a specific occurrence at a specific point in space and time.
A Call-type Event is meant to call an operation, and cannot instantiate a Signal at the same time.
Add a reference to an Operation, if the Event doesn’t have one.
An Event instantiating a Signal should be a Signal-type Event.