Serializing Option<T> type in protocol buffer

I have a type that's

 public class Option<T> 
 {
     private bool _hasValue;
     private T _value;
     private Option(T val) { _value = val; _hasValue = true; }
     private Option(bool hasValue) { _hasValue = hasValue; }
     
     public static Option<T> Value(T val) => return new Option(val);
     public static Option<T> Nothing() => return new Option(false);
 }

I wish I could serialize this using protobuf just like a Nullable<T>. ie. is there a way to provide protobuf-net with a custom serializer, that would output nothing if _hasValue is false and that would output the serialized version of _val if _hasValue is true?

Sorry can't seem to find the doc to do this.