Header.unapply return type makes pattern matches non-exhaustive

[nigredo-tori]

Header.unapply returns an Option. From the compiler's point of view, this means that it can potentially fail - meaning a pattern match like this

header match {
  case Header(_, _) => ???
}

is non-exhaustive, and triggers the corresponding compiler lint.

We can fix this by changing the return type of unapply to Some[(String, String)] - see this Scastie.