Further generic-ify `reaction_users` `after` param

Further generic-ify the `after` parameter on the `reaction_users` method
of the following structs:

- `ChannelId`
- `Group`
- `GuildChannel`
- `Message`
- `Channel`
- `GuildChannel`

Do this by changing the `U` trait bound from `Into<UserId>` to
`Into<Option<UserId>>`.

This resolves problems determining types when passing `None` as the
argument, as reported in #247.

1 files changed, 8 insertions, 8 deletions

diff --git a/src/model/channel/mod.rs b/src/model/channel/mod.rs
index 00fc7f6..1a6bcd5 100644
--- a/src/model/channel/mod.rs
+++ b/src/model/channel/mod.rs
@@ -371,14 +371,14 @@ impl Channel {
     #[deprecated(since = "0.4.2", note = "Use the inner channel's method")]
     #[inline]
     pub fn reaction_users<M, R, U>(&self,
-                                   message_id: M,
-                                   reaction_type: R,
-                                   limit: Option<u8>,
-                                   after: Option<U>)
-                                   -> Result<Vec<User>>
-        where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.id()
-            .reaction_users(message_id, reaction_type, limit, after)
+        message_id: M,
+        reaction_type: R,
+        limit: Option<u8>,
+        after: U,
+    ) -> Result<Vec<User>> where M: Into<MessageId>,
+                                 R: Into<ReactionType>,
+                                 U: Into<Option<UserId>> {
+        self.id().reaction_users(message_id, reaction_type, limit, after)
     }
 
     /// Retrieves the Id of the inner [`Group`], [`GuildChannel`], or