@Override
    public Class convert(String value) {

        if (isBlank(value)) {
            throw new ParameterException(getErrorString("a blank value", "a class"));
        }

        try {
            return Class.forName(value);
        } catch (ClassNotFoundException e) {
            throw new ParameterException(getErrorString(value, "a class"));
        }
    }
@Test(expected = ParameterException.class)
    public void nullValueThrowsParameterException() {
        converter.convert(null);
    }