"FailWhen" to drop out if a certain condition is met

[sameera]

It is quite common to be writing code that looks like:

getSomething()
  .Map(something => {
    if (!someCondition(something)) {
     return Outcome<Something>.Reject("Description of failure");
    }
    return doSomething(something);
}

FailWhen will simplify this to:

getSomething()
  .FailWhen(something => !someCondition(something), "Description of failure");
  .Map(something => doSomething(something));