shrink method

@override Iterable<Shrinkable<T?>> shrink()

Generates an Iterable of Shrinkables that fulfill the following criteria:

• They are similar to this: They only differ in little ways.
• They are simpler than this: The transitive hull is finite acyclic. If you would call shrink on all returned values and on the values returned by them etc., this process should terminate sometime.

Implementation

@override
Iterable<Shrinkable<T?>> shrink() {
  final shrinkableNull = Shrinkable<T?>(null, () => []);
  return originalValue
      .shrink()
      .cast<Shrinkable<T?>>()
      .followedBy([shrinkableNull]);
}