Question

I have this code :

private MyClass CreateObject(MyOtherClass myOtherClass)
{
    return new MyClass
    {
        Name = myOtherClass.Name,
        ValidationDate = (DateTime)myOtherClass.ValidationDate  //ValidationDate is nullable
    };
}

If I do this, I have a compilation error :

Type of conditional expression cannot be determined because there is
no implicit conversion between '<null>' and 'System.DateTime'

private MyClass CreateObject(MyOtherClass myOtherClass)
{
    return new MyClass
    {
        Name = myOtherClass.Name,
        ValidationDate = (myOtherClass.VALIDATION_DATE == null) ? null : DateTime.Now  //ValidationDate is nullable
    };
}

If I do this, no problem :

MyClass myClass = new MyClass();
if (myClass.ValidationDate == null)
    myClass.ValidationDate = null;

The question is why ? and Solustion ? 🙂

Answer 1

The problem in the first code block is that you’re trying to cast a nullable DateTime value to DateTime.

Try casting it to nullable DateTime (DateTime?) instead:

ValidationDate = (DateTime?)myOtherClass.ValidationDate

because you’re trying to populate a nullable DateTime field after all.

If you’re trying to provide a default value in case myOtherClass.ValidationDate is null, then use the coalescing operator (no casts needed):

ValidationDate = myOtherClass.ValidationDate ?? DateTime.Now