@Override
    public Map<String, Set<ExecutableElement>> setters() {
      return Maps.transformValues(
          classifier.propertyNameToSetters().asMap(),
          propertySetters ->
              propertySetters.stream().map(PropertySetter::getSetter).collect(toSet()));
    }
Representation of an {@code AutoValue.Builder} class or interface.
value/src/main/java/com/google/auto/value/processor/BuilderSpec.java