[MM-17300] Do not add empty string as a keyword key (#11961)

* Do not add empty string as a keyword key

* Add unit test

* User assert lib over t.Fatal

app/notification.go

@@ -593,7 +593,9 @@ func (a *App) getMentionKeywordsInChannel(profiles map[string]*model.User, lookF
 			for _, k := range splitKeys {
 				// note that these are made lower case so that we can do a case insensitive check for them
 				key := strings.ToLower(k)
-				keywords[key] = append(keywords[key], id)
+				if key != "" {
+					keywords[key] = append(keywords[key], id)
+				}
 			}
 		}
 

app/notification_test.go

@@ -1150,6 +1150,29 @@ func TestGetMentionKeywords(t *testing.T) {
 	} else if _, ok := mentions["@here"]; ok {
 		t.Fatal("should not have mentioned any user with @here")
 	}
+
+	// user with empty mention keys
+	userNoMentionKeys := &model.User{
+		Id:        model.NewId(),
+		FirstName: "First",
+		Username:  "User",
+		NotifyProps: map[string]string{
+			"mention_keys": ",",
+		},
+	}
+
+	channelMemberNotifyPropsMapEmptyOff := map[string]model.StringMap{
+		userNoMentionKeys.Id: {
+			"ignore_channel_mentions": model.IGNORE_CHANNEL_MENTIONS_OFF,
+		},
+	}
+
+	profiles = map[string]*model.User{userNoMentionKeys.Id: userNoMentionKeys}
+	mentions = th.App.getMentionKeywordsInChannel(profiles, true, channelMemberNotifyPropsMapEmptyOff)
+	assert.Equal(t, 1, len(mentions), "should've returned one metion keyword")
+	ids, ok := mentions["@user"]
+	assert.True(t, ok)
+	assert.Equal(t, userNoMentionKeys.Id, ids[0], "should've returned mention key of @user")
 }
 
 func TestGetMentionsEnabledFields(t *testing.T) {