private static String builderInitializer(
        AnnotatedTypeMirror annotatedType, Optional<String> nullableAnnotation) {
      if (nullableAnnotation.isPresent()) {
        return "";
      }
      Optionalish optional = Optionalish.createIfOptional(annotatedType.getType());
      if (optional == null) {
        return "";
      }
      return " = " + optional.getEmpty();
    }
Returns the appropriate initializer for a builder property. The caller of the {@code
Property} constructor may have supplied an initializer, but otherwise we supply one only if
this property is an {@code Optional} and is not {@code @Nullable}. In that case the
initializer sets it to {@code Optional.empty()}.
value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java