Clean up code somewhat.

app/models/commit.rb

@@ -139,15 +139,14 @@ class Commit
     users << author
     users << committer
     
-    mentions = []
-    mentions << self.mentioned_users(current_user, project)
+    users.push *self.mentioned_users(current_user, project)
 
     notes(project).each do |note|
       users << note.author
-      mentions << note.mentioned_users(current_user, project)
+      users.push *note.mentioned_users(current_user, project)
     end
 
-    users.concat(mentions.reduce([], :|)).uniq
+    users.uniq
   end
 
   def notes(project)

app/models/concerns/issuable.rb

@@ -122,16 +122,15 @@ module Issuable
     users = []
     users << author
     users << assignee if is_assigned?
-    
-    mentions = []
-    mentions << self.mentioned_users(current_user)
+
+    users.push *self.mentioned_users(current_user)
 
     notes.each do |note|
       users << note.author
-      mentions << note.mentioned_users(current_user)
+      users.push *note.mentioned_users(current_user)
     end
 
-    users.concat(mentions.reduce([], :|)).uniq
+    users.uniq
   end
 
   def subscribed?(user)

app/models/snippet.rb

@@ -90,15 +90,13 @@ class Snippet < ActiveRecord::Base
   def participants(current_user = self.author)
     users = []
     users << author
-
-    mentions = []
     
     notes.each do |note|
       users << note.author
-      mentions << note.mentioned_users(current_user)
+      users.push *note.mentioned_users(current_user)
     end
 
-    users.concat(mentions.reduce([], :|)).uniq
+    users.uniq
   end
 
   class << self

app/services/projects/participants_service.rb

@@ -13,19 +13,21 @@ module Projects
     end
 
     def participants_in(type, id)
-      users = case type
-              when "Issue"
-                issue = project.issues.find_by_iid(id)
-                issue ? issue.participants(current_user) : []
-              when "MergeRequest"
-                merge_request = project.merge_requests.find_by_iid(id)
-                merge_request ? merge_request.participants(current_user) : []
-              when "Commit"
-                commit = project.repository.commit(id)
-                commit ? commit.participants(project, current_user) : []
-              else
-                []
-              end
+      users = 
+        case type
+        when "Issue"
+          issue = project.issues.find_by_iid(id)
+          issue.participants(current_user) if issue
+        when "MergeRequest"
+          merge_request = project.merge_requests.find_by_iid(id)
+          merge_request.participants(current_user) if merge_request
+        when "Commit"
+          commit = project.repository.commit(id)
+          commit.participants(project, current_user) if commit
+        end
+
+      return [] unless users
+      
       sorted(users)
     end