Adds the Rubocop ReturnNil cop

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

lib/gitlab/i18n/metadata_entry.rb

@@ -15,7 +15,7 @@ module Gitlab
       end
       def expected_forms
-        return nil unless plural_information
+        return unless plural_information
         plural_information['nplurals'].to_i
       end

lib/gitlab/import_export/json_hash_builder.rb

@@ -67,7 +67,7 @@ module Gitlab
       # +value+ existing model to be included in the hash
       # +parsed_hash+ the original hash
       def parse_hash(value)
-        return nil if already_contains_methods?(value)
+        return if already_contains_methods?(value)
         @attributes_finder.parse(value) do |hash|
           { include: hash_or_merge(value, hash) }

lib/gitlab/import_export/relation_factory.rb

@@ -75,7 +75,7 @@ module Gitlab
       # the relation_hash, updating references with new object IDs, mapping users using
       # the "members_mapper" object, also updating notes if required.
       def create
-        return nil if unknown_service?
+        return if unknown_service?
         setup_models

lib/gitlab/incoming_email.rb

@@ -57,7 +57,7 @@ module Gitlab
       def address_regex
         wildcard_address = config.address
-        return nil unless wildcard_address
+        return unless wildcard_address
         regex = Regexp.escape(wildcard_address)
         regex = regex.sub(Regexp.escape(WILDCARD_PLACEHOLDER), '(.+)')

lib/gitlab/legacy_github_import/client.rb

@@ -68,7 +68,7 @@ module Gitlab
       end
       def user(login)
-        return nil unless login.present?
+        return unless login.present?
         return @users[login] if @users.key?(login)
         @users[login] = api.user(login)

lib/gitlab/legacy_github_import/user_formatter.rb

@@ -25,7 +25,7 @@ module Gitlab
       end
       def find_by_email
-        return nil unless email
+        return unless email
         User.find_by_any_email(email)
             .try(:id)
@@ -33,7 +33,7 @@ module Gitlab
       # rubocop: disable CodeReuse/ActiveRecord
       def find_by_external_uid
-        return nil unless id
+        return unless id
         identities = ::Identity.arel_table

lib/gitlab/sql/pattern.rb

@@ -33,7 +33,7 @@ module Gitlab
         #                     `LOWER(column) = query` instead of using `ILIKE`.
         def fuzzy_arel_match(column, query, lower_exact_match: false)
           query = query.squish
-          return nil unless query.present?
+          return unless query.present?
           words = select_fuzzy_words(query)

lib/gitlab/tracing/jaeger_factory.rb

@@ -60,7 +60,7 @@ module Gitlab
         elsif udp_endpoint.present?
           sender = get_udp_sender(encoder, udp_endpoint)
         else
-          return nil
+          return
         end
         Jaeger::Reporters::RemoteReporter.new(

lib/gitlab/tree_summary.rb

@@ -95,7 +95,7 @@ module Gitlab
     end
     def cache_commit(commit)
-      return nil unless commit.present?
+      return unless commit.present?
       resolved_commits[commit.id] ||= commit
     end

lib/system_check/app/git_user_default_ssh_config_check.rb

@@ -53,7 +53,7 @@ module SystemCheck
       end
       def ssh_dir
-        return nil unless home_dir
+        return unless home_dir
         File.join(home_dir, '.ssh')
       end

spec/support/import_export/export_file_helper.rb

@@ -91,7 +91,7 @@ module ExportFileHelper
     loop do
       object_with_parent = deep_find_with_parent(sensitive_word, project_hash)
-      return nil unless object_with_parent && object_with_parent.object
+      return unless object_with_parent && object_with_parent.object
       if is_safe_hash?(object_with_parent.parent, sensitive_word)
         # It's in the safe list, remove hash and keep looking