code: ImmutableSortedSet<String> typesToImport() {
      ImmutableSortedSet.Builder<String> typesToImport = ImmutableSortedSet.naturalOrder();
      for (Map.Entry<String, Spelling> entry : imports.entrySet()) {
        if (entry.getValue().importIt) {
          typesToImport.add(entry.getKey());
        }
      }
      return typesToImport.build();
    }
docs: Returns the set of types to import. We import every type that is neither in java.lang nor in
  the package containing the AutoValue class, provided that the result refers to the type
  unambiguously. For example, if there is a property of type java.util.Map.Entry then we will
  import java.util.Map.Entry and refer to the property as Entry. We could also import just
  java.util.Map in this case and refer to Map.Entry, but currently we never do that.