Document when Events::PaymentSent::pending_fee_msat is Some

lightning/src/events/mod.rs

@@ -789,6 +789,8 @@ pub enum Event {
 		/// If the recipient or an intermediate node misbehaves and gives us free money, this may
 		/// overstate the amount paid, though this is unlikely.
 		///
+		/// This is only `None` for payments initiated on LDK versions prior to 0.0.103.
+		///
 		/// [`Route::get_total_fees`]: crate::routing::router::Route::get_total_fees
 		fee_paid_msat: Option<u64>,
 	},

lightning/src/ln/outbound_payment.rs

@@ -71,7 +71,7 @@ pub(crate) enum PendingOutboundPayment {
 		keysend_preimage: Option<PaymentPreimage>,
 		custom_tlvs: Vec<(u64, Vec<u8>)>,
 		pending_amt_msat: u64,
-		/// Used to track the fee paid. Only present if the payment was serialized on 0.0.103+.
+		/// Used to track the fee paid. Present iff the payment was serialized on 0.0.103+.
 		pending_fee_msat: Option<u64>,
 		/// The total payment amount across all paths, used to verify that a retry is not overpaying.
 		total_msat: u64,