added validations for billing address

src/main/java/com/nisum/paymentvendorsimulator/creditcard/domain/dto/CreditCardAddress.java

@@ -5,17 +5,28 @@ import lombok.Getter;
 import lombok.NoArgsConstructor;
 import lombok.Setter;
 
+import javax.validation.constraints.NotBlank;
+
 @Getter
 @Setter
 @AllArgsConstructor
 @NoArgsConstructor
 public class CreditCardAddress {
 
+  @NotBlank(message = "addressLine1 cannot be left blank")
   private String addressLine1;
+
   private String addressLine2;
+
+  @NotBlank(message = "cityName cannot be left blank")
   private String cityName;
+
   private String countryCode;
+
+  @NotBlank(message = "countryName cannot be left blank")
   private String countryName;
+
+  @NotBlank(message = "postalCode cannot be left blank")
   private String postalCode;
 
 }

src/main/java/com/nisum/paymentvendorsimulator/creditcard/domain/dto/CreditCardAmount.java

@@ -17,7 +17,7 @@ public class CreditCardAmount {
   @Pattern(regexp = "\\d+\\.\\d{2}", message="Value must be at dollar and cents value separated by '.'")
   String value;
 
-  @NotBlank
+  @NotBlank(message = "currency cannot be left blank")
   String currency;
 
 }

src/main/java/com/nisum/paymentvendorsimulator/creditcard/domain/dto/CreditCardData.java

@@ -26,7 +26,7 @@ public class CreditCardData {
   @Pattern(regexp = "\\d{3}", message = "cvc must be 3 digits")
   String cvc;
 
-  @NotBlank
+  @NotBlank(message = "holderName cannot be left blank")
   String holderName;
 
 }

src/main/java/com/nisum/paymentvendorsimulator/creditcard/domain/dto/CreditCardRequest.java

@@ -26,7 +26,7 @@ public class CreditCardRequest {
   @NotBlank(message="merchantAccount can't be blank")
   String merchantAccount;
 
+  @Valid
   CreditCardAddress billingAddress;
 
-
 }