Added implicit headOption method SCALA-334

Author: rozza

docs/reference/content/changelog.md

@@ -12,6 +12,7 @@ Changes between released versions
 
 ### 2.2.0
 
+  * Added implicit headOption method [SCALA-334](https://jira.mongodb.org/browse/SCALA-334)
   * Added BsonProperty annotation [SCALA-321](https://jira.mongodb.org/browse/SCALA-321)
   * Updated Mongodb Driver Async dependency to [3.5.0](https://jira.mongodb.org/browse/SCALA-335)
   * CaseClassCodec - Added support for internal vals. [SCALA-314](https://jira.mongodb.org/browse/SCALA-314)

driver/src/main/scala/org/mongodb/scala/ObservableImplicits.scala

@@ -347,6 +347,7 @@ trait ObservableImplicits {
      * @return the head result of the [[Observable]].
      */
     def head(): Future[T] = {
+      import scala.concurrent.ExecutionContext.Implicits.global
       headOption().map {
         case Some(result) => result
         case None => null.asInstanceOf[T]  // scalastyle:ignore null

driver/src/test/scala/org/mongodb/scala/internal/ScalaObservableSpec.scala

@@ -384,6 +384,17 @@ class ScalaObservableSpec extends FlatSpec with Matchers {
     errorSeen.getOrElse(None) shouldBe a[Throwable]
   }
 
+  it should "provide a headOption method" in {
+    Await.result(observable[Int]().headOption(), Duration(10, TimeUnit.SECONDS)) should equal(Some(1))
+    Await.result(observable[Int](fail = true).headOption(), Duration(10, TimeUnit.SECONDS)) should equal(Some(1))
+
+    intercept[MongoException] {
+      Await.result(TestObservable[Int](Observable[Int](1 to 10), failOn = 1).headOption(), Duration(10, TimeUnit.SECONDS))
+    }
+
+    Await.result(TestObservable[Int](Observable(List[Int]())).headOption(), Duration(10, TimeUnit.SECONDS)) should equal(None)
+  }
+
   it should "provide a head method" in {
     Await.result(observable[Int]().head(), Duration(10, TimeUnit.SECONDS)) should equal(1)
     Await.result(observable[Int](fail = true).head(), Duration(10, TimeUnit.SECONDS)) should equal(1)