add validation

src/main/java/com/faf223/expensetrackerfaf/model/User.java

@@ -1,6 +1,8 @@
 package com.faf223.expensetrackerfaf.model;
 
 import jakarta.persistence.*;
+import jakarta.validation.constraints.NotEmpty;
+import jakarta.validation.constraints.NotNull;
 import lombok.*;
 
 import java.util.List;
@@ -17,15 +19,23 @@ public class User {
     private String userUuid;
 
     @Column(name = "name")
+    @NotNull(message = "First name must not be null")
+    @NotEmpty(message = "First name must not be empty")
     private String firstName;
 
     @Column(name = "surname")
+    @NotNull(message = "Last name must not be null")
+    @NotEmpty(message = "Last name must not be empty")
     private String lastName;
 
     @Column(name = "username")
+    @NotNull(message = "Username must not be null")
+    @NotEmpty(message = "Username must not be empty")
     private String username;
 
     @Transient
+    @NotNull(message = "Password must not be null")
+    @NotEmpty(message = "Password must not be empty")
     private String password;
 
     @OneToMany(mappedBy = "user", fetch = FetchType.LAZY)