@Override
  public Blob getBlob() throws LayerPropertyNotFoundException {
    throw new LayerPropertyNotFoundException("Blob not available for reference layer");
  }
Instantiate with a {@link BlobDescriptor} and diff ID.

@param blobDescriptor the blob descriptor
@param diffId the diff ID
jib-core/src/main/java/com/google/cloud/tools/jib/image/ReferenceLayer.java