| [AutoValue](https://github.com/google/auto/tree/master/value) instances should |
| be deeply immutable. Therefore, we recommend using immutable types for fields. |
| E.g., use `ImmutableMap` instead of `Map`, `ImmutableSet` instead of `Set`, etc. |
| |
| Read more at: |
| |
| * https://github.com/google/auto/blob/master/value/userguide/practices.md#avoid-mutable-property-types |
| * https://github.com/google/auto/blob/master/value/userguide/builders-howto.md#-use-a-collection-valued-property |
| |
| Suppress violations by using `@SuppressWarnings("AutoValueImmutableFields")` on |
| the relevant `abstract` getter. |
