public void CleanTest()
        {
            NullBooleanField target = new NullBooleanField();

            Assert.AreEqual(false, target.Clean(false));
            Assert.AreEqual(false, target.Clean(bool.FalseString));
            Assert.AreEqual(false, target.Clean("0"));
            Assert.AreEqual(false, target.Clean(0));
            Assert.AreEqual(false, target.Clean("off"));

            Assert.AreEqual(true, target.Clean(true));
            Assert.AreEqual(true, target.Clean(bool.TrueString));
            Assert.AreEqual(true, target.Clean("1"));
            Assert.AreEqual(true, target.Clean(1));
            Assert.AreEqual(true, target.Clean("on"));

            Assert.IsNull(target.Clean(null));
            Assert.IsNull(target.Clean("asdfakjsdfaksjdhf"));
            Assert.IsNull(target.Clean(string.Empty));
            Assert.IsNull(target.Clean(" "));
        }