code: public static void checkContentType(String contentType) {
      Preconditions.checkArgument(contentType != null); // for backwards compatibility
      Preconditions.checkArgument(
          HttpMediaType.equalsIgnoreParameters(MEDIA_TYPE, contentType),
          "Wrong content type: expected <" + MEDIA_TYPE + "> but got <%s>",
          contentType);
    }
docs: Checks the given content type matches the Atom content type specified in {@link #MEDIA_TYPE}.
  
  @throws IllegalArgumentException if content type doesn't match