Revert Handle NPE caused by SingleResultCallback based Observables

SCALA-568

Author: rozza

docs/reference/content/changelog.md

@@ -10,6 +10,9 @@ title = "Changelog"
 
 Changes between released versions
 
+### 2.9.0
+  * Revert Handle NPE caused by SingleResultCallback based Observables [SCALA-568](https://jira.mongodb.org/browse/SCALA-568F)
+
 ### 2.8.0
   * Updated MongoDB Driver Async to 3.12.0
   * Refined GridFS binary stream interchange in GridFS [SCALA-569](https://jira.mongodb.org/browse/SCALA-569)

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

@@ -442,10 +442,7 @@ trait ObservableImplicits {
             subscription.request(1)
           }
 
-          override def onError(throwable: Throwable): Unit = throwable match {
-            case npe: NullPointerException => onComplete()
-            case _                         => completeWith("onError", () => observer.onError(throwable))
-          }
+          override def onError(throwable: Throwable): Unit = completeWith("onError", () => observer.onError(throwable))
 
           override def onComplete(): Unit = {
             completeWith("onComplete", { () =>