Object reference not set to an instance of an object - ASP.NET

Question

I have a controller class inside my ASP.NET server and I'm trying to get a list of all the data inside a table in my MySQL database. But for some reason my context variable inside my controller is null.

The error (on my context variable):

Object reference not set to an instance of an object

My controller class:

using Dyslexia.Managers;
using Dyslexia.Models;
using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;

namespace Dyslexia.Controllers
{
    public class SchoolController : Controller
    {
        [HttpGet]
        [Route("Api/Schools")]
        public IEnumerable<SchoolModel> GetAllSchools()
        {
            SchoolManager context = HttpContext.RequestServices.GetService(typeof(SchoolManager)) as SchoolManager;
            return context.GetAllSchools().ToArray();
        }
    }
}

My SchoolManager class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Dyslexia.Models;
using Microsoft.AspNetCore.Mvc;
using MvcSakilaCore.Models;
using MySql.Data.MySqlClient;

namespace Dyslexia.Managers
{
    public class SchoolManager
    {
        public string ConnectionString { get; set; }

        public SchoolManager(string connectionString)
        {
            ConnectionString = connectionString;
        }

        private MySqlConnection GetConnection()
        {
            return new MySqlConnection(ConnectionString);
        }

        public List<SchoolModel> GetAllSchools()
        {
            List<SchoolModel> schoolsList = new List<SchoolModel>();

            using (MySqlConnection dbConnection = GetConnection())
            {
                dbConnection.Open();
                MySqlCommand cmd = new MySqlCommand("SELECT * FROM schools", dbConnection);

                using (MySqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        schoolsList.Add(new SchoolModel()
                        {
                            Id = reader.GetInt32("Id"),
                            Name = reader.GetString("Name"),
                            Address = reader.GetString("Address"),
                            City = reader.GetString("City"),
                            PhoneNumber = reader.GetString("PhoneNumber"),
                            State = reader.GetString("State"),
                            Country = reader.GetString("Country"),
                            Zip = reader.GetString("Zip"),
                            AdminId = reader.GetInt32("AdminId"),
                            Active = reader.GetInt32("Active"),
                        });
                    }
                }
            }

            return schoolsList;
        }
    }
}