Adds the Rubocop ReturnNil cop

This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points

.rubocop.yml

@@ -181,3 +181,6 @@ Cop/InjectEnterpriseEditionModule:
   Exclude:
     - 'spec/**/*'
     - 'ee/spec/**/*'
+
+Style/ReturnNil:
+  Enabled: true

app/controllers/concerns/continue_params.rb

@@ -6,7 +6,7 @@ module ContinueParams
   def continue_params
     continue_params = params[:continue]
-    return nil unless continue_params
+    return unless continue_params
     continue_params = continue_params.permit(:to, :notice, :notice_now)
     continue_params[:to] = safe_redirect_path(continue_params[:to])

app/controllers/concerns/renders_notes.rb

@@ -16,7 +16,7 @@ module RendersNotes
   private
   def preload_max_access_for_authors(notes, project)
-    return nil unless project
+    return unless project
     user_ids = notes.map(&:author_id)
     project.team.max_member_access_for_user_ids(user_ids)

app/controllers/projects/application_controller.rb

@@ -17,7 +17,7 @@ class Projects::ApplicationController < ApplicationController
   def project
     return @project if @project
-    return nil unless params[:project_id] || params[:id]
+    return unless params[:project_id] || params[:id]
     path = File.join(params[:namespace_id], params[:project_id] || params[:id])
     auth_proc = ->(project) { !project.pending_delete? }

app/controllers/projects/merge_requests/diffs_controller.rb

@@ -46,8 +46,8 @@ class Projects::MergeRequests::DiffsController < Projects::MergeRequests::Applic
   # rubocop: disable CodeReuse/ActiveRecord
   def commit
-    return nil unless commit_id = params[:commit_id].presence
-    return nil unless @merge_request.all_commits.exists?(sha: commit_id)
+    return unless commit_id = params[:commit_id].presence
+    return unless @merge_request.all_commits.exists?(sha: commit_id)
     @commit ||= @project.commit(commit_id)
   end

app/controllers/uploads_controller.rb

@@ -28,13 +28,13 @@ class UploadsController < ApplicationController
   end
   def find_model
-    return nil unless params[:id]
+    return unless params[:id]
     upload_model_class.find(params[:id])
   end
   def authorize_access!
-    return nil unless model
+    return unless model
     authorized =
       case model
@@ -54,7 +54,7 @@ class UploadsController < ApplicationController
   end
   def authorize_create_access!
-    return nil unless model
+    return unless model
     # for now we support only personal snippets comments
     authorized = can?(current_user, :comment_personal_snippet, model)

app/helpers/markup_helper.rb

@@ -74,7 +74,7 @@ module MarkupHelper
   # the tag contents are truncated without removing the closing tag.
   def first_line_in_markdown(object, attribute, max_chars = nil, options = {})
     md = markdown_field(object, attribute, options)
-    return nil unless md.present?
+    return unless md.present?
     tags = %w(a gl-emoji b pre code p span)
     tags << 'img' if options[:allow_images]

app/helpers/merge_requests_helper.rb

@@ -29,7 +29,7 @@ module MergeRequestsHelper
   def ci_build_details_path(merge_request)
     build_url = merge_request.source_project.ci_service.build_page(merge_request.diff_head_sha, merge_request.source_branch)
-    return nil unless build_url
+    return unless build_url
     parsed_url = URI.parse(build_url)
@@ -92,7 +92,7 @@ module MergeRequestsHelper
   end
   def version_index(merge_request_diff)
-    return nil if @merge_request_diffs.empty?
+    return if @merge_request_diffs.empty?
     @merge_request_diffs.size - @merge_request_diffs.index(merge_request_diff)
   end
@@ -149,7 +149,7 @@ module MergeRequestsHelper
   def merge_request_source_project_for_project(project = @project)
     unless can?(current_user, :create_merge_request_in, project)
-      return nil
+      return
     end
     if can?(current_user, :create_merge_request_from, project)

app/helpers/notes_helper.rb

@@ -122,7 +122,7 @@ module NotesHelper
   end
   def new_form_url
-    return nil unless @snippet.is_a?(PersonalSnippet)
+    return unless @snippet.is_a?(PersonalSnippet)
     snippet_notes_path(@snippet)
   end

app/models/ci/build.rb

@@ -735,7 +735,7 @@ module Ci
     # Virtual deployment status depending on the environment status.
     def deployment_status
-      return nil unless starts_environment?
+      return unless starts_environment?
       if success?
         return successful_deployment_status

app/models/commit_range.rb

@@ -134,25 +134,25 @@ class CommitRange
   end
   def sha_from
-    return nil unless @commit_from
+    return unless @commit_from
     @commit_from.id
   end
   def sha_to
-    return nil unless @commit_to
+    return unless @commit_to
     @commit_to.id
   end
   def sha_start
-    return nil unless sha_from
+    return unless sha_from
     exclude_start? ? sha_from + '^' : sha_from
   end
   def commit_start
-    return nil unless sha_start
+    return unless sha_start
     if exclude_start?
       @commit_start ||= project.commit(sha_start)

app/models/concerns/blob_language_from_git_attributes.rb

@@ -5,7 +5,7 @@ module BlobLanguageFromGitAttributes
   extend ActiveSupport::Concern
   def language_from_gitattributes
-    return nil unless project
+    return unless project
     repository = project.repository
     repository.gitattribute(path, 'gitlab-language')

app/models/concerns/feature_gate.rb

@@ -2,7 +2,7 @@
 module FeatureGate
   def flipper_id
-    return nil if new_record?
+    return if new_record?
     "#{self.class.name}:#{id}"
   end

app/models/concerns/mirror_authentication.rb

@@ -79,7 +79,7 @@ module MirrorAuthentication
   end
   def ssh_public_key
-    return nil if ssh_private_key.blank?
+    return if ssh_private_key.blank?
     comment = "git@#{::Gitlab.config.gitlab.host}"
     ::SSHKey.new(ssh_private_key, comment: comment).ssh_public_key

app/models/concerns/reactive_caching.rb

@@ -69,7 +69,7 @@ module ReactiveCaching
     def with_reactive_cache(*args, &blk)
       unless within_reactive_cache_lifetime?(*args)
         refresh_reactive_cache!(*args)
-        return nil
+        return
       end
       keep_alive_reactive_cache!(*args)

app/models/environment.rb

@@ -119,7 +119,7 @@ class Environment < ActiveRecord::Base
   def first_deployment_for(commit_sha)
     ref = project.repository.ref_name_for_sha(ref_path, commit_sha)
-    return nil unless ref
+    return unless ref
     deployment_iid = ref.split('/').last
     deployments.find_by(iid: deployment_iid)
@@ -130,7 +130,7 @@ class Environment < ActiveRecord::Base
   end
   def formatted_external_url
-    return nil unless external_url
+    return unless external_url
     external_url.gsub(%r{\A.*?://}, '')
   end

app/models/label_note.rb

@@ -81,7 +81,7 @@ class LabelNote < Note
     deleted = label_refs.count - existing_refs.count
     deleted_str = deleted == 0 ? nil : "#{deleted} deleted"
-    return nil unless refs_str || deleted_str
+    return unless refs_str || deleted_str
     label_list_str = [refs_str, deleted_str].compact.join(' + ')
     suffix = 'label'.pluralize(deleted > 0 ? deleted : existing_refs.count)

app/models/legacy_diff_note.rb

@@ -73,7 +73,7 @@ class LegacyDiffNote < Note
   private
   def find_diff
-    return nil unless noteable
+    return unless noteable
     return @diff if defined?(@diff)
     @diff = noteable.raw_diffs(Commit.max_diff_options).find do |d|

app/models/namespace.rb

@@ -149,7 +149,7 @@ class Namespace < ApplicationRecord
   end
   def find_fork_of(project)
-    return nil unless project.fork_network
+    return unless project.fork_network
     if Gitlab::SafeRequestStore.active?
       forks_in_namespace = Gitlab::SafeRequestStore.fetch("namespaces:#{id}:forked_projects") do

app/models/notification_recipient.rb

@@ -119,7 +119,7 @@ class NotificationRecipient
   private
   def read_ability
-    return nil if @skip_read_ability
+    return if @skip_read_ability
     return @read_ability if instance_variable_defined?(:@read_ability)
     @read_ability =
@@ -136,7 +136,7 @@ class NotificationRecipient
   end
   def default_project
-    return nil if @target.nil?
+    return if @target.nil?
     return @target if @target.is_a?(Project)
     return @target.project if @target.respond_to?(:project)
   end