do not link non existant functions in the base library

src/commands/mod.rs

@@ -62,6 +62,8 @@ macro_rules! derive_command_into_packet {
                 #[doc = "Tries to turn a [`" $command_type "`] into a [Packet]."]
                 ///
                 /// Returns: NULL or a [Packet] containing the command.
+                ///
+                /// [Packet]: [`servicepoint::Packet`]
                 fn try_into_packet(move instance) -> move_ok *mut ::servicepoint::Packet {
                     instance.try_into()
                 };