Unwraps an optional and throws error if nil. The related blogpost: https://kelindev.blogspot.com/2018/01/catching-nil-as-error.html.

Unwrap.swift

func unwrap<T>(_ optional: T?) throws -> T {
  if let real = optional {
    return real
  } else {
    throw UnwrapError(optional: optional)
  }
}

struct UnwrapError<T>: Error, CustomStringConvertible {
  let optional: T?
  
  public var description: String {
    return "Found nil while unwrapping \(String(describing: optional))!"
  }
}