Fixed errors

API/Controllers/SubjectsController.cs

@@ -1,12 +1,9 @@
-using System;
+using System.Collections.Generic;
-using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Authorization;
-using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
-using Newtonsoft.Json;
 using StudyLib.API.Data;
 using StudyLib.Models;
 
@@ -123,7 +120,7 @@ namespace StudyLib.API.Controllers
 
             await _context.SaveChangesAsync();
 
-            return CreatedAtAction("GetSubject", new { id = subject.ID }, subject);
+            return NoContent();
         }
 
         // DELETE: api/Subjects/5