Error: string[] does not contain a definition for 'Contains' - works and doesn't work

Question

Working on an MVC5 app. I'm a little confused by this one.... I have 2 variables, both defined as string arrays (msUsers and msSites). One, msUsers, allows me to use "Contains", the other doesn't. Here's a snippet of the code....

    private IQueryable<Event> GetEventsFiltered(
        string userName,
        string workStatus,
        string[] msUsers,
        string[] msSites,
        int? eventTypeId)
    {
        IQueryable<Event> events = this.db.Events;

        if (msUsers != null)
        {
            events = events.Include(a => a.AspNetUser)
                .Where(a => msUsers.Contains(a.AspNetUser.Id));
        }

        if (msSites != null)
        {
            // It doesn't like Contains here....
            events = events.Include(a => a.Branch)
                .Where(a => msSites.Contains(a.Branch.Id));
        }

The error (for the last "Contains")...

 'string[]' does not contain a definition for 'Contains' and the best extension method 
  overload 'Queryable.Contains<int>(IQueryable<int>, int)' requires a receiver of type 
  'IQueryable<int>'

I'm a little confused because the first usage of Contains works fine against the SAME type of variable. Any suggestions/ideas? Thanks!

***** UPDATED to add NAMESPACES ******

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Net;
using System.Web.Mvc;
using System.Web.Security;

using AuditingApp.Models;
using AuditingApp.Services;
using AuditingApp.ViewModels;

using Microsoft.AspNet.Identity;

Answer 1

The error is indicating a type mismatch, basically. Your database column for Branch.id is an integer, and your msSites[] is a string array. You are trying to use Contains to compare a string to an int without doing type conversion.

Option 1 Since the id appears to always be an int, you can refactor your method to accept int[] msSites and that would likely resolve the problem.

Option 2 If you can't change the argument types to your method, you could try converting a.Branch.Id to a string in the Contains call.