Nullable DateTime deserialization issue

[pieceofsummer]

[Fact]
public void Deserialize_CorrectlyDeserializes_NullableDateTime()
{
    var value = DateTime.Now;
    var serializedData = new InvocationData(
        typeof(InvocationDataFacts).AssemblyQualifiedName,
        nameof(NullableDateTimeMethod),
        JobHelper.ToJson(new[] { typeof(DateTime?) }),
        JobHelper.ToJson(new[] { value.ToString("o", CultureInfo.InvariantCulture) }));

    var job = serializedData.Deserialize(); // throws
    
    Assert.Equal(value, job.Args[0]);
}

or even simpler:

[Fact]
public void Deserialize_CorrectlyDeserializes_NullableDateTime()
{
    var value = DateTime.Now;
    var job = Job.FromExpression(() => NullableDateTimeMethod(value));
    var invocationData = InvocationData.Serialize(job);

    var job2 = invocationData.Deserialize(); // throws

    Assert.Equal(value, job2.Args[0]);
}

[plaisted]

Was just working on DateTime for #971 , might as well through this fix in as well.