docs: private static String format(@Nullable final Class<?> expectedType, @Nullable final Class<?> actualType) {
  		final String expected = expectedType != null ? expectedType.getName() : NO_TYPE_PLACEHOLDER;
  		final String actual = actualType != null ? actualType.getName() : NO_TYPE_PLACEHOLDER;
  		return String.format(MESSAGE_WITH_TYPES, expected, actual);
  	}