code: @Nonnull
    public static <T> T checkNotNull(@Nullable T obj) {
      return checkNotNull(obj, NPE_DEFAULT_MSG);
    }
docs: Throws a NullPointerException with a generic message if the specified object is {@code null}, otherwise
  returns it.
  
  @param obj an object of any type or {@code null}
  @param <T> any type
  
  @return the argument