problem fixed for migration from redmine 3.x to redmine 4

CHANGELOG.rst

@@ -6,6 +6,7 @@ Changelog
 
 - Performance improvement (#36)
 - FontAwesome 5.6.3 support
+- Fix problem from migrating from Redmine 3.x to Redmine 4 with lost settings
 
 2.0.17
 ++++++

lib/additionals.rb

@@ -56,10 +56,18 @@ module Additionals
     end
 
     def settings
-      if Rails.version >= '5.2'
-        Setting[:plugin_additionals]
+      if Setting[:plugin_additionals].class == Hash
+        if Rails.version >= '5.2'
+          # convert Rails 4 data
+          new_settings = ActiveSupport::HashWithIndifferentAccess.new(Setting[:plugin_additionals])
+          Setting.plugin_additionals = new_settings
+          new_settings
+        else
+          ActionController::Parameters.new(Setting[:plugin_additionals])
+        end
       else
-        ActionController::Parameters.new(Setting[:plugin_additionals])
+        # Rails 5 uses ActiveSupport::HashWithIndifferentAccess
+        Setting[:plugin_additionals]
       end
     end