From 7680146f85b05775a2fdeac9e9b20983cb43bf59 Mon Sep 17 00:00:00 2001
From: Joost Pastoor <joost.pastoor@munisense.com>
Date: Sat, 13 Jun 2020 09:27:39 +0200
Subject: [PATCH 1/3] Add .idea to the .gitignore

---
 .gitignore | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.gitignore b/.gitignore
index 48b8bf9..ae09aba 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 vendor/
+.idea
\ No newline at end of file

From 3afb6aefab8b9149f47fcab0bf2d13b454bfd9f1 Mon Sep 17 00:00:00 2001
From: Joost Pastoor <joost.pastoor@munisense.com>
Date: Sat, 13 Jun 2020 09:28:05 +0200
Subject: [PATCH 2/3] Synced the lockfile of Gopkg

---
 Gopkg.lock | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/Gopkg.lock b/Gopkg.lock
index 2930c69..214e4e9 100644
--- a/Gopkg.lock
+++ b/Gopkg.lock
@@ -1,33 +1,69 @@
 # This file is autogenerated, do not edit; changes may be undone by the next 'dep ensure'.
 
 
+[[projects]]
+  digest = "1:e0419edd44e362e2ab972a6f68c91a20adaa79ff24a6fd511055d1f0fcd93b79"
+  name = "github.com/graph-gophers/dataloader"
+  packages = ["."]
+  pruneopts = ""
+  revision = "78139374585c29dcb97b8f33089ed11959e4be59"
+  version = "v5"
+
 [[projects]]
   branch = "master"
+  digest = "1:43987212a2f16bfacc1a286e9118f212d60c136ed53c6c9477c18921db53140b"
   name = "github.com/hashicorp/golang-lru"
-  packages = [".","simplelru"]
+  packages = [
+    ".",
+    "simplelru",
+  ]
+  pruneopts = ""
   revision = "0a025b7e63adc15a622f29b0b2c4c3848243bbf6"
 
 [[projects]]
+  digest = "1:e0419edd44e362e2ab972a6f68c91a20adaa79ff24a6fd511055d1f0fcd93b79"
+  name = "github.com/nicksrandall/dataloader"
+  packages = ["."]
+  pruneopts = ""
+  revision = "78139374585c29dcb97b8f33089ed11959e4be59"
+  version = "v5"
+
+[[projects]]
+  digest = "1:78fb99d6011c2ae6c72f3293a83951311147b12b06a5ffa43abf750c4fab6ac5"
   name = "github.com/opentracing/opentracing-go"
-  packages = [".","log"]
+  packages = [
+    ".",
+    "log",
+  ]
+  pruneopts = ""
   revision = "1949ddbfd147afd4d964a9f00b24eb291e0e7c38"
   version = "v1.0.2"
 
 [[projects]]
+  digest = "1:4c0404dc03d974acd5fcd8b8d3ce687b13bd169db032b89275e8b9d77b98ce8c"
   name = "github.com/patrickmn/go-cache"
   packages = ["."]
+  pruneopts = ""
   revision = "a3647f8e31d79543b2d0f0ae2fe5c379d72cedc0"
   version = "v2.1.0"
 
 [[projects]]
   branch = "master"
+  digest = "1:447831205e1c85dbf1e6f97cb8ca54931452c6aff79c630ea091ecbbdc2e921e"
   name = "golang.org/x/net"
   packages = ["context"]
+  pruneopts = ""
   revision = "a8b9294777976932365dabb6640cf1468d95c70f"
 
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "a0b8606d9f2ed9df7e69cae570c65c7d7b090bb7a08f58d3535b584693d44da9"
+  input-imports = [
+    "github.com/graph-gophers/dataloader",
+    "github.com/hashicorp/golang-lru",
+    "github.com/nicksrandall/dataloader",
+    "github.com/opentracing/opentracing-go",
+    "github.com/patrickmn/go-cache",
+  ]
   solver-name = "gps-cdcl"
   solver-version = 1

From 98e283a5696b7249f50b22fab0c49eea6bf294b0 Mon Sep 17 00:00:00 2001
From: Joost Pastoor <joost.pastoor@munisense.com>
Date: Sat, 13 Jun 2020 09:28:41 +0200
Subject: [PATCH 3/3] Prevent panic when batchloader returns nil values by
 replacing them with Result errors

---
 dataloader.go      |  7 +++++++
 dataloader_test.go | 50 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/dataloader.go b/dataloader.go
index 8f04581..d210103 100644
--- a/dataloader.go
+++ b/dataloader.go
@@ -460,6 +460,13 @@ func (b *batcher) batch(originalContext context.Context) {
 		return
 	}
 
+	// When a batchFunc returns a nil in it's items, we replace those by a Result struct containing an error
+	for key, value := range items {
+		if value == nil {
+			items[key] = &Result{Error: fmt.Errorf("no value for key")}
+		}
+	}
+
 	for i, req := range reqs {
 		req.channel <- items[i]
 		close(req.channel)
diff --git a/dataloader_test.go b/dataloader_test.go
index d676731..9c97afe 100644
--- a/dataloader_test.go
+++ b/dataloader_test.go
@@ -211,6 +211,32 @@ func TestLoader(t *testing.T) {
 		// TODO: expect to get some kind of warning
 	})
 
+	t.Run("first result is a nil", func(t *testing.T) {
+		t.Parallel()
+		faultyLoader, _ := LoaderNilInsteadOfResult()
+		ctx := context.Background()
+
+		n := 10
+		reqs := []Thunk{}
+		keys := Keys{}
+		for i := 0; i < n; i++ {
+			key := StringKey(strconv.Itoa(i))
+			reqs = append(reqs, faultyLoader.Load(ctx, key))
+			keys = append(keys, key)
+		}
+
+		for i, future := range reqs {
+			_, err := future()
+			if i == 0 && err == nil {
+				t.Error("expected first result to contain an error")
+			}
+
+			if i != 0 && err != nil {
+				t.Error("expected rest of results not to contain an error")
+			}
+		}
+	})
+
 	t.Run("responds to max batch size", func(t *testing.T) {
 		t.Parallel()
 		identityLoader, loadCalls := IDLoader(2)
@@ -586,6 +612,30 @@ func FaultyLoader() (*Loader, *[][]string) {
 	return loader, &loadCalls
 }
 
+// LoaderNilInsteadOfResult gives a nil result back for the first key.
+func LoaderNilInsteadOfResult() (*Loader, *[][]string) {
+	var mu sync.Mutex
+	var loadCalls [][]string
+
+	loader := NewBatchedLoader(func(_ context.Context, keys Keys) []*Result {
+		var results []*Result
+		mu.Lock()
+		loadCalls = append(loadCalls, keys.Keys())
+		mu.Unlock()
+
+		for i, key := range keys {
+			if i == 0 {
+				results = append(results, nil)
+			} else {
+				results = append(results, &Result{key, nil})
+			}
+		}
+		return results
+	})
+
+	return loader, &loadCalls
+}
+
 ///////////////////////////////////////////////////
 // Benchmarks
 ///////////////////////////////////////////////////