Nil.reduce throws UnsupportedOperationException instead of NoSuchElementException

Author: xirc

core/src/main/scala/scala/collection/parallel/ParIterableLike.scala

@@ -358,6 +358,8 @@ extends IterableOnce[T @uncheckedVariance]
    *  if this $coll is empty.
    */
   def reduce[U >: T](op: (U, U) => U): U = {
+    if (isEmpty) throw new UnsupportedOperationException("empty.reduce")
+
     tasksupport.executeAndWaitResult(new Reduce(op, splitter)).get
   }
 

junit/src/test/scala/scala/collection/parallel/mutable/ParArrayTest.scala

@@ -85,6 +85,11 @@ class ParArrayTest extends scala.collection.concurrent.ctries_old.Spec {
     assert( ParArray(1,2,3,4,5).reduce(_+_) == 15 )
   }
 
+  @Test
+  def `empty reduce`: Unit = {
+    evaluating { ParArray.empty[Int].reduce(_+_) }.shouldProduce[UnsupportedOperationException]()
+  }
+
   @Test
   def `simple count`: Unit = {
     assert( ParArray[Int]().count(_ > 7) == 0 )