State<T>.Is Unknown(T) Method
Test to see if the field value form state has a value.
public bool IsUnknown (T state);
abstract member IsUnknown : 'T -> bool
Public Function IsUnknown (state As T) As Boolean
Form state to check.
True if value is unknown.
For value types (numbers, bools, date time) a value is unknown only if the field is nullable and it is null.
For enum based values (both simple and enumerated) they can also be nullable or the 0 enum value if not nullable.
For non value types like string the test is to see if the field is actually null.