[Bug] if an Enum field is optional and has null value, the TryGet function should return false but not true.

[JustusPan]

if an Enum field is optional, when it's value is null
fields.TryGetEnum("KeyType", out var keyType)
then the return value of this TryGet should be false
but currently it returns true

[Cammin]

In the XML documentation and the API docs, the return value is described as returning true if the field exists.