@Override
  public void serialize(
      DescriptorDigest value, JsonGenerator jsonGenerator, SerializerProvider ignored)
      throws IOException {
    jsonGenerator.writeString(value.toString());
  }
Serializes a {@link DescriptorDigest} into JSON element.
jib-core/src/main/java/com/google/cloud/tools/jib/image/json/DescriptorDigestSerializer.java