Pattern Matching to check if string is null or empty

def isNullOrEmpty[T](s: Seq[T]) = s match {
     case null => true
     case Seq() => true
     case _ => false
}

You can write a simple function like:

def isEmpty(x: String) = Option(x).forall(_.isEmpty)

or

def isEmpty(x: String) = x == null || x.isEmpty

You might also want to trim the string, if you consider " " to be empty as well.

def isEmpty(x: String) = x == null || x.trim.isEmpty

and then use it

val messageId = message.identifier
messageId match {
  case id if isEmpty(id) => validate()
  case id => // blabla
}

or without a match

if (isEmpty(messageId)) {
  validate()
} else {
  // blabla
}

or even

object EmptyString {
  def unapply(s: String): Option[String] =
    if (s == null || s.trim.isEmpty) Some(s) else None
}

message.identifier match {
  case EmptyString(s) => validate()
  case _ => // blabla
}