Strilanc.Value.May<T>.Match() - Must never use null as second parameter

the May type from the Strilang.Value package has two overloads for the Match() function.

1. `May.Match(Func valueProjection, Func alternativeFunc)`
1. `May.Match(Func valueProjection, TOut alternativeValue)`

The first variant must not be called with `alternativeFunc` being `null`. The second may be called with null, but if written as plain code, using `null` here the compiler usually resolves it to the first variant, and by that failing at runtime.

Project on GitHub: https://github.com/Strilanc
Package in NuGet: https://www.nuget.org/packages/Strilanc.Value.May