public Optional<FilePropertiesSpec> getProperties() {
    return Optional.ofNullable(properties);
  }
Constructor for use by jackson to populate this object.

@param entries a list of {@link LayerSpec} defining the layers in this container
@param properties a {@link FilePropertiesSpec} that applies to all layers in this buildfile
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/buildfile/LayersSpec.java