Use (immutable) user ID instead of (mutable) screen name

lib/twitter/rest/lists.rb

@@ -477,10 +477,12 @@ def merge_list!(hash, list) # rubocop:disable MethodLength
       # @param user[Integer, String, Twitter::User] A Twitter user ID, screen_name, or object.
       # @return [Hash]
       def merge_owner!(hash, user)
-        unless hash[:owner_id] || hash[:owner_screen_name]
-          user ||= screen_name
+        return hash if hash[:owner_id] || hash[:owner_screen_name]
+        if user
           merge_user!(hash, user, 'owner')
           hash[:owner_id] = hash.delete(:owner_user_id) unless hash[:owner_user_id].nil?
+        else
+          hash[:owner_id] = user_id
         end
         hash
       end

lib/twitter/rest/users.rb

@@ -252,8 +252,8 @@ def users(*args)
       #   @option options [Boolean, String, Integer] :skip_status Do not include user's Tweets when set to true, 't' or 1.
       def user(*args)
         arguments = Twitter::Arguments.new(args)
-        if arguments.last || screen_name?
-          merge_user!(arguments.options, arguments.pop || screen_name)
+        if arguments.last || user_id?
+          merge_user!(arguments.options, arguments.pop || user_id)
           perform_with_object(:get, '/1.1/users/show.json', arguments.options, Twitter::User)
         else
           verify_credentials(arguments.options)
@@ -375,7 +375,7 @@ def update_profile_banner(banner, options = {})
       #   @param user [Integer, String, Twitter::User] A Twitter user ID, screen name, URI, or object.
       def profile_banner(*args)
         arguments = Twitter::Arguments.new(args)
-        merge_user!(arguments.options, arguments.pop || screen_name) unless arguments.options[:user_id] || arguments.options[:screen_name]
+        merge_user!(arguments.options, arguments.pop || user_id) unless arguments.options[:user_id] || arguments.options[:screen_name]
         perform_with_object(:get, '/1.1/users/profile_banner.json', arguments.options, Twitter::ProfileBanner)
       end
     end

lib/twitter/rest/utils.rb

@@ -75,7 +75,7 @@ def parallel_user_objects_from_response(request_method, path, args)
       # @return [Array<Twitter::User>]
       def user_objects_from_response(request_method, path, args)
         arguments = Twitter::Arguments.new(args)
-        merge_user!(arguments.options, arguments.pop || screen_name) unless arguments.options[:user_id] || arguments.options[:screen_name]
+        merge_user!(arguments.options, arguments.pop || user_id) unless arguments.options[:user_id] || arguments.options[:screen_name]
         perform_with_objects(request_method, path, arguments.options, Twitter::User)
       end
 
@@ -110,16 +110,16 @@ def parallel_objects_from_response(klass, request_method, path, args)
       # @return [Twitter::Cursor]
       def cursor_from_response_with_user(collection_name, klass, request_method, path, args) # rubocop:disable ParameterLists
         arguments = Twitter::Arguments.new(args)
-        merge_user!(arguments.options, arguments.pop || screen_name) unless arguments.options[:user_id] || arguments.options[:screen_name]
+        merge_user!(arguments.options, arguments.pop || user_id) unless arguments.options[:user_id] || arguments.options[:screen_name]
         perform_with_cursor(request_method, path, arguments.options, collection_name, klass)
       end
 
-      def screen_name
-        @screen_name ||= verify_credentials.screen_name
+      def user_id
+        @user_id ||= verify_credentials.id
       end
 
-      def screen_name?
-        instance_variable_defined?(:@screen_name)
+      def user_id?
+        instance_variable_defined?(:@user_id)
       end
 
       def merge_default_cursor!(options)