Prevent NPE in GroupContext

group_blackbox_test.go

@@ -105,3 +105,18 @@ func TestGroupContextWithError(t *testing.T) {
 	assertEqual(t, int32(5), atomic.LoadInt32(&startedCount))
 	assertEqual(t, int32(4), atomic.LoadInt32(&doneCount))
 }
+
+func TestGroupContextWithNilContext(t *testing.T) {
+
+	pool := pond.New(3, 100)
+
+	var thrownPanic interface{}
+	func() {
+		defer func() {
+			thrownPanic = recover()
+		}()
+		pool.GroupContext(nil)
+	}()
+
+	assertEqual(t, "a non-nil context needs to be specified when using GroupContext", thrownPanic)
+}

pond.go

@@ -492,6 +492,11 @@ func (p *WorkerPool) Group() *TaskGroup {
 // The derived Context is canceled the first time a function submitted to the group
 // returns a non-nil error or the first time Wait returns, whichever occurs first.
 func (p *WorkerPool) GroupContext(ctx context.Context) (*TaskGroupWithContext, context.Context) {
+
+	if ctx == nil {
+		panic("a non-nil context needs to be specified when using GroupContext")
+	}
+
 	ctx, cancel := context.WithCancel(ctx)
 	return &TaskGroupWithContext{
 		TaskGroup: TaskGroup{