add validation

src/main/java/com/faf223/expensetrackerfaf/dto/UserDTO.java

@@ -1,14 +1,21 @@
 package com.faf223.expensetrackerfaf.dto;
 
+import jakarta.validation.constraints.NotEmpty;
+import jakarta.validation.constraints.NotNull;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 
 @Data
 @AllArgsConstructor
 public class UserDTO {
-
+    @NotNull(message = "Name must not be null")
+    @NotEmpty(message = "Name must not be empty")
     private String name;
+    @NotNull(message = "Surname must not be null")
+    @NotEmpty(message = "Surname must not be empty")
     private String surname;
+    @NotNull(message = "Username must not be null")
+    @NotEmpty(message = "Username must not be empty")
     private String username;
 
 }