code: public static void noNullElements(Collection<?> c, String message) {
          if (c != null) {
              for (Object element : c) {
                  if (element == null) {
                      throw new IllegalArgumentException(message);
                  }
              }
          }
      }
docs: Assert that a {@link java.util.Collection} has no null elements.
  
  @param c the collection to check
  @param message the exception message to use if the assertion fails
  @throws IllegalArgumentException if the {@link Collection} contains a {@code null} element