From 877e1b7f9ae59b840eafa082e6fe1c64e1db637b Mon Sep 17 00:00:00 2001
From: George Goldberg <george@gberg.me>
Date: Thu, 22 Nov 2018 11:19:47 +0000
Subject: [PATCH] MM-12957: Fix moving a channel with no members. (#9841)

---
 app/channel.go      | 14 ++++++++------
 app/channel_test.go | 21 +++++++++++++++++++--
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/app/channel.go b/app/channel.go
index 6e4f1b103a..318ceb10cf 100644
--- a/app/channel.go
+++ b/app/channel.go
@@ -1709,13 +1709,15 @@ func (a *App) MoveChannel(team *model.Team, channel *model.Channel, user *model.
 		channelMemberIds = append(channelMemberIds, channelMember.UserId)
 	}
 
-	teamMembers, err2 := a.GetTeamMembersByIds(team.Id, channelMemberIds)
-	if err2 != nil {
-		return err2
-	}
+	if len(channelMemberIds) > 0 {
+		teamMembers, err2 := a.GetTeamMembersByIds(team.Id, channelMemberIds)
+		if err2 != nil {
+			return err2
+		}
 
-	if len(teamMembers) != len(*channelMembers) {
-		return model.NewAppError("MoveChannel", "app.channel.move_channel.members_do_not_match.error", nil, "", http.StatusInternalServerError)
+		if len(teamMembers) != len(*channelMembers) {
+			return model.NewAppError("MoveChannel", "app.channel.move_channel.members_do_not_match.error", nil, "", http.StatusInternalServerError)
+		}
 	}
 
 	// keep instance of the previous team
diff --git a/app/channel_test.go b/app/channel_test.go
index 9acf8a709d..d31318fe3d 100644
--- a/app/channel_test.go
+++ b/app/channel_test.go
@@ -8,10 +8,11 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/mattermost/mattermost-server/model"
-	"github.com/mattermost/mattermost-server/store"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/store"
 )
 
 func TestPermanentDeleteChannel(t *testing.T) {
@@ -138,6 +139,22 @@ func TestMoveChannel(t *testing.T) {
 	if err := th.App.MoveChannel(targetTeam, channel2, th.BasicUser, true); err != nil {
 		t.Fatal(err)
 	}
+
+	// Test moving a channel with no members.
+	channel3 := &model.Channel{
+		DisplayName: "dn_" + model.NewId(),
+		Name:        "name_" + model.NewId(),
+		Type:        model.CHANNEL_OPEN,
+		TeamId:      sourceTeam.Id,
+		CreatorId:   th.BasicUser.Id,
+	}
+
+	var err *model.AppError
+	channel3, err = th.App.CreateChannel(channel3, false)
+	require.Nil(t, err)
+
+	err = th.App.MoveChannel(targetTeam, channel3, th.BasicUser, false)
+	assert.Nil(t, err)
 }
 
 func TestJoinDefaultChannelsCreatesChannelMemberHistoryRecordTownSquare(t *testing.T) {