Added some nullable regions to get rid of compiler warnings and follow best practices

ScrumTaskboard/Controllers/CategoriesController.cs

@@ -19,6 +19,7 @@ namespace ScrumTaskboard.Controllers
         }
 
         // GET: api/category
+        #nullable enable
         [HttpGet]
         public async Task<ActionResult<IEnumerable<ScrumCategory>>> GetCategory([FromQuery]string? title, [FromQuery]int? projectid, [FromQuery] string? color)
         {
@@ -40,6 +41,7 @@ namespace ScrumTaskboard.Controllers
 
             return await filtered.ToListAsync();
         }
+        #nullable disable
 
         // GET: api/category/1
         [HttpGet("{id}")]