[FIX] Error when updating omnichannel department without agents parameter (#18428)

* Fix error when updating department through REST API.

* Improves validation of endpoint parameters

app/livechat/server/lib/Helper.js

@@ -379,6 +379,10 @@ export const updateDepartmentAgents = (departmentId, agents) => {
 	}
 
 	upsert.forEach((agent) => {
+		if (!Users.findOneById(agent.agentId, { fields: { _id: 1 } })) {
+			return;
+		}
+
 		LivechatDepartmentAgents.saveAgent({
 			agentId: agent.agentId,
 			departmentId,
@@ -400,4 +404,6 @@ export const updateDepartmentAgents = (departmentId, agents) => {
 		const numAgents = LivechatDepartmentAgents.find({ departmentId }).count();
 		LivechatDepartment.updateNumAgentsById(departmentId, numAgents);
 	}
+
+	return true;
 };

app/livechat/server/lib/Livechat.js

@@ -813,22 +813,22 @@ export const Livechat = {
 	saveDepartmentAgents(_id, departmentAgents) {
 		check(_id, String);
 		check(departmentAgents, {
-			upsert: [
+			upsert: Match.Maybe([
 				Match.ObjectIncluding({
 					agentId: String,
 					username: String,
 					count: Match.Maybe(Match.Integer),
 					order: Match.Maybe(Match.Integer),
 				}),
-			],
-			remove: [
+			]),
+			remove: Match.Maybe([
 				Match.ObjectIncluding({
 					agentId: String,
 					username: Match.Maybe(String),
 					count: Match.Maybe(Match.Integer),
 					order: Match.Maybe(Match.Integer),
 				}),
-			],
+			]),
 		});
 
 		const department = LivechatDepartment.findOneById(_id);
@@ -836,8 +836,7 @@ export const Livechat = {
 			throw new Meteor.Error('error-department-not-found', 'Department not found', { method: 'livechat:saveDepartmentAgents' });
 		}
 
-		const departmentDB = LivechatDepartment.createOrUpdateDepartment(_id, department);
-		return departmentDB && updateDepartmentAgents(departmentDB._id, departmentAgents);
+		return updateDepartmentAgents(_id, departmentAgents);
 	},
 
 	saveDepartment(_id, departmentData, departmentAgents) {
@@ -880,7 +879,7 @@ export const Livechat = {
 		}
 
 		const departmentDB = LivechatDepartment.createOrUpdateDepartment(_id, departmentData);
-		if (departmentDB) {
+		if (departmentDB && departmentAgents) {
 			updateDepartmentAgents(departmentDB._id, departmentAgents);
 		}