private String getGeneratedTypeName() {
    return generatedAnnotation(elementUtils, processingEnv.getSourceVersion())
        .map(generatedAnnotation -> TypeEncoder.encode(generatedAnnotation.asType()))
        .orElse("");
  }
Issue a compilation error and return an exception that, when thrown, will cause the processing
of this class to be abandoned. This does not prevent the processing of other classes.
value/src/main/java/com/google/auto/value/processor/AutoAnnotationProcessor.java