Gadget preference value containing spaces gets corrupted

When gadget is maximised request parameter containing spaces (actually + symbol) e.g. targetGroup=Media+and+Messaging+Media+Platforms, becomes incorrectly encoded, e.g. targetGroup=Media%2Band%2BMessaging%2BMedia%2BPlatforms

Problem is originally reported with jira-timesheet-plugin gadget option that allows to select jira group. Option value (gadget preference value) is group name in the case and is stored in literal. I was not able to find JIRA standard gadget with similar case.

Steps to reproduce.

Prerequisites:
1. JIRA group containing spaces, e.g. Media and Messaging Media Platforms
2. Time Sheet gadget on dashboard from jira-timesheet-plugin

Scenario:
1. Configure gadget, see 'Show summary for users in groups' option and select group containing spaces
2. Open developer tools in browser and see gadget request, e.g.: http://localhost/jira/rest/timesheet-gadget/1.0/timesheet.json?targetGroup=Media+and+Messaging+Media+Platforms
3. Click maximize, and see request having incorrect parameter: http://localhost/jira/rest/timesheet-gadget/1.0/timesheet.json?targetGroup=Media%2Band%2BMessaging%2BMedia%2BPlatforms

Expected: the same request parameter value as before maximising gadget.

Note, that having + sign in group name does not get incorrectly encoded when maximising.