@Override
public void undo() {
this.assignment.setDiagram(null);
BehavioralPattern diagram = ((BehavioralPattern) getBehavioralPatternEditPart().getModel());
diagram.getFragments().remove(this.assignment);
this.assignment.setLeftSide(null);
this.assignment.setRightSide(null);
this.assignment.setParentOperand(null);
this.assignment.setLifeline(null);
super.undo();
}
