code: public void assertDoesNotHaveDuplicates(Description description, Collection<?> actual) {
      assertNotNull(description, actual);
      Collection<?> duplicates = duplicatesFrom(actual);
      if (duplicates.isEmpty()) {
        return;
      }
      throw failures.failure(description, shouldNotHaveDuplicates(actual, duplicates));
    }
docs: Asserts that the given {@code Collection} does not have duplicate values.
  
  @param description contains information about the assertion.
  @param actual      the given {@code Collection}.
  @throws NullPointerException     if the array of values is {@code null}.
  @throws IllegalArgumentException if the array of values is empty.
  @throws AssertionError           if the given {@code Collection} is {@code null}.
  @throws AssertionError           if the given {@code Collection} contains duplicate values.