add validation

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

@@ -1,6 +1,8 @@
 package com.faf223.expensetrackerfaf.dto;
 
 import com.faf223.expensetrackerfaf.model.IncomeCategory;
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotNull;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 
@@ -10,9 +12,19 @@ import java.time.LocalDate;
 @Data
 @AllArgsConstructor
 public class IncomeDTO {
+    @NotNull(message = "ID must not be null")
     private long incomeId;
+
+    @NotNull(message = "User must not be null")
     private UserDTO userDTO;
+
+    @NotNull(message = "Category must not be null")
     private IncomeCategory incomeCategory;
+
+    @NotNull(message = "Date must not be null")
     private LocalDate date;
+
+    @NotNull(message = "Amount must not be null")
+    @DecimalMin(value = "0.0", inclusive = false, message = "Amount must be positive")
     private BigDecimal amount;
 }