Optional Codable property issue

[admkopec]

After dropping CodableBox a new issue arose when declaring entity attribute as an optional codable type. The NSAttributeDescription's isOptional value is set to false, which is invalid and results in "NSLocalizedDescription=%{PROPERTY}@ is a required value., NSValidationErrorKey=optionalSip, NSValidationErrorValue=null" error upon save when the attribute value is nil.

[admkopec]

I was able to quickly isolate the issue to the getter of valueType. When no attributeValueClassName is present, then this getter returns Any. But it should return Any or Any? depending on value of isOptional.

I'll try to make a quick PR for this.