code: public static void notEmpty(Collection collection, String message) {
          if (Collections.isEmpty(collection)) {
              throw new IllegalArgumentException(message);
          }
      }
docs: Assert that a collection has elements; that is, it must not be
  <code>null</code> and must have at least one element.
  <pre class="code">Assert.notEmpty(collection, "Collection must have elements");</pre>
  @param collection the collection to check
  @param message the exception message to use if the assertion fails
  @throws IllegalArgumentException if the collection is <code>null</code> or has no elements