code: @Override
    public Collection<Spec> getAllVersionsOfSpec(URI specUri) {
      Preconditions.checkArgument(null != specUri, "Spec URI should not be null");
      Path specPath = getPathForURI(this.fsSpecStoreDirPath, specUri, FlowSpec.Builder.DEFAULT_VERSION);
      return getAllVersionsOfSpec(specPath);
    }
docs: Returns all versions of the spec defined by specUri.
  Currently, multiple versions are not supported, so this should return exactly one spec.
  @param specUri URI for the {@link Spec} to be retrieved.
  @return all versions of the spec.