Even though the underlying type includes an option, most users should not have to think about the difference between Some "" and None. You can use the Expert module to deal with the optionality, if need be.
Some ""
None
Expert
val to_bigstring_shared_option : t ‑> Email_message.Bigstring_shared.t option
val of_bigstring_shared_option : Email_message.Bigstring_shared.t option ‑> t