Avoid using head

When retrieving the head of a sequence, use headOption rather than head.

Reason

Some collections are empty, and head deals with them by throwing an exception:

Seq.empty[Int].head
// java.util.NoSuchElementException: head of empty list
// 	at scala.collection.immutable.Nil$.head(List.scala:430)
// 	at scala.collection.immutable.Nil$.head(List.scala:427)
// 	at repl.Session$App$$anonfun$1.apply$mcI$sp(traversable_head.md:9)
// 	at repl.Session$App$$anonfun$1.apply(traversable_head.md:9)
// 	at repl.Session$App$$anonfun$1.apply(traversable_head.md:9)

headOption is a safer alternative, since it encodes the possibility of the empty list in its return type:

Seq(1, 2, 3).headOption
// res0: Option[Int] = Some(1)

Seq.empty[Int].headOption
// res1: Option[Int] = None

Checked by

Linter	Rule
Scapegoat	TraversableHead
WartRemover	TraversableOps