refactor: add an understanding of nullable for swagger gen

ApiDto/Responses/GroupResponse.cs

@@ -1,4 +1,6 @@
-namespace Mirea.Api.Dto.Responses;
+using System.ComponentModel.DataAnnotations;
+
+namespace Mirea.Api.Dto.Responses;
 
 /// <summary>
 /// Represents basic information about a group.
@@ -8,16 +10,19 @@ public class GroupResponse
     /// <summary>
     /// Gets or sets the unique identifier of the group.
     /// </summary>
+    [Required]
     public int Id { get; set; }
 
     /// <summary>
     /// Gets or sets the name of the group.
     /// </summary>
+    [Required]
     public required string Name { get; set; }
 
     /// <summary>
     /// Gets or sets the course number of the group.
     /// </summary>
+    [Required]
     public int CourseNumber { get; set; }
 
     /// <summary>