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

@@ -123,15 +123,14 @@ module Issuable
     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

@@ -91,14 +91,12 @@ class Snippet < ActiveRecord::Base
     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
+      users = 
+        case type
         when "Issue"
           issue = project.issues.find_by_iid(id)
-                issue ? issue.participants(current_user) : []
+          issue.participants(current_user) if issue
         when "MergeRequest"
           merge_request = project.merge_requests.find_by_iid(id)
-                merge_request ? merge_request.participants(current_user) : []
+          merge_request.participants(current_user) if merge_request
         when "Commit"
           commit = project.repository.commit(id)
-                commit ? commit.participants(project, current_user) : []
-              else
-                []
+          commit.participants(project, current_user) if commit
         end
+
+      return [] unless users
+      
       sorted(users)
     end