add validation

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

@@ -1,16 +1,19 @@
 package com.faf223.expensetrackerfaf.dto;
 
-import com.faf223.expensetrackerfaf.model.IncomeCategory;
-import com.faf223.expensetrackerfaf.model.User;
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotNull;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 
 import java.math.BigDecimal;
-import java.time.LocalDate;
 
 @Data
 @AllArgsConstructor
 public class IncomeCreationDTO {
+    @NotNull(message = "Category must not be null")
     private int incomeCategory;
+
+    @NotNull(message = "Amount must not be null")
+    @DecimalMin(value = "0.0", inclusive = false, message = "Amount must be positive")
     private BigDecimal amount;
 }