From 47ab16c2bf7dd92fe616be7e614c3ddb72003f5a Mon Sep 17 00:00:00 2001
From: Alejandro Durante <alitto@gmail.com>
Date: Mon, 9 May 2022 20:24:36 -0300
Subject: [PATCH] Prevent NPE in GroupContext

---
 group_blackbox_test.go | 15 +++++++++++++++
 pond.go                |  5 +++++
 2 files changed, 20 insertions(+)

diff --git a/group_blackbox_test.go b/group_blackbox_test.go
index 306f832..0f04f11 100644
--- a/group_blackbox_test.go
+++ b/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)
+}
diff --git a/pond.go b/pond.go
index d025b12..307d710 100644
--- a/pond.go
+++ b/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{