Change (Set<Relation> removedRelations, Set<Relation> addedRelations, DfType oldType, DfType newType) { if (removedRelations.isEmpty() && addedRelations.isEmpty() && oldType == DfType.BOTTOM && newType == DfType.BOTTOM) { return null; } return new Change(removedRelations, addedRelations, oldType, newType); }