Get right value from either in languageExt

I have object:

public Either<Error, Provider> Provider { get; set; }

public class Provider
{

   public string Name { get; set; }

   public decimal? Amount { get; set; }
}

How do I get only the right value? I tried:

source.Provider.Map(x => x.Amount)

source.Provider.Select(x => x.Amount)

but when there's no value I get exception that the value is null, though I'd like it to be null so I could compare it later:

if (source.Provider.Select(x => x.Amount) != old.Price)
{
   ....
}