Abc.Maybe (nuget): Provides a fully-featured Option type, aka a Maybe type, with several companion helpers (parsing, LINQ).  An Option type allows to represent objects that are either something (a value or a reference) or nothing. Nullable Reference Types (NRT) do not count since they are not actual .NET types but annotations that are ignored at run-time.  A tutorial along with guidelines is available on the project website.
Keywords: Option|Maybe|Nullable|LINQ|ROP|Railway|Monad|linq|maybe|monad|optional|rop