Address review comments

Author: AnuthaDev

Diff for: crates/router/src/types/api/payment_methods.rs

@@ -68,18 +68,23 @@ impl PaymentMethodCreateExt for PaymentMethodCreate {
 #[cfg(all(feature = "v2", feature = "payment_methods_v2"))]
 impl PaymentMethodCreateExt for PaymentMethodCreate {
     fn validate(&self) -> RouterResult<()> {
-        self.payment_method_subtype.map(|pm_subtype| {
-            if !validate_payment_method_type_against_payment_method(
-                self.payment_method_type,
-                pm_subtype,
-            ) {
-                return Err(report!(errors::ApiErrorResponse::InvalidRequestData {
+        utils::when(
+            !self
+                .payment_method_subtype
+                .map(|sub| {
+                    validate_payment_method_type_against_payment_method(
+                        self.payment_method_type,
+                        sub,
+                    )
+                })
+                .unwrap_or(true), // If payment_method_subtype is None, we assume it to be valid
+            || {
+                Err(report!(errors::ApiErrorResponse::InvalidRequestData {
                     message: "Invalid 'payment_method_type' provided".to_string()
                 })
-                .attach_printable("Invalid payment method type"));
-            }
-            Ok(())
-        });
+                .attach_printable("Invalid payment method type"))
+            },
+        )?;
 
         utils::when(
             !Self::validate_payment_method_data_against_payment_method(