Resolve "OutgoingAuthorities event is triggered too many times."

Closes #281 (closed)

Closes #243 (closed)

pallets/authority-members/src/lib.rs

@@ -580,20 +580,24 @@ impl<T: Config> pallet_session::SessionManager<T::ValidatorId> for Pallet<T> {
         for member_id in members_ids_to_add.iter() {
             T::OnIncomingMember::on_incoming_member(*member_id);
         }
-        // a single event with all authorities
-        Self::deposit_event(Event::IncomingAuthorities {
-            members: members_ids_to_add.clone(),
-        });
+        // a single event with all authorities if some
+        if !members_ids_to_add.is_empty() {
+            Self::deposit_event(Event::IncomingAuthorities {
+                members: members_ids_to_add.clone(),
+            });
+        }
 
         // -- handle outgoing members
         // callback when smith is outgoing
         for member_id in members_ids_to_del.iter() {
             T::OnOutgoingMember::on_outgoing_member(*member_id);
         }
-        // a single event with all authorities
-        Self::deposit_event(Event::OutgoingAuthorities {
-            members: members_ids_to_del.clone(),
-        });
+        // a single event with all authorities if some
+        if !members_ids_to_del.is_empty() {
+            Self::deposit_event(Event::OutgoingAuthorities {
+                members: members_ids_to_del.clone(),
+            });
+        }
 
         // updates the list of OnlineAuthorities and returns the list of their key
         Some(