Activiti-admin does not support Latin special characters

Description
The activiti-admin application doesn't support Latin characters, such as ç, ã and other accented characters. For example, if a process has tasks with Portuguese characters in their name, searching for those tasks is throwing an error in the activiti-admin UI.

Steps to reproduce
1. Via App Designer in activiti-app import 'çãçãçãçãçãçãçãçãçã.zip' and publish application attached
NOTE: The app comes with a simple process: Start event -> user task -> end event
The user task has a name "çãçãçãçãçãçãçãçãçã".
2. From the published app on the landing page start 4 process instances creating a total of 4 tasks then.
3. Log into activiti-admin and via the "Tasks" tab use the filter´s name field and type in "çãçãçãçãçãçãçãçãçã"

Expected Behaviour
All tasks containing Latin characters should be returned.

Observed Behaviour
It's NOT possible to search for tasks containing Latin characters, a red error bar is displayed with message:

"An error occured while calling Activiti: HTTP/1.1 400 Bad Request"

 
Supporting evidence

• Reproduced with current latest APS 1.9.0.3 release
• Inspected the Tomcat access log and can see the RETS call failing with status 400:

  127.0.0.1 - - [28/Nov/2018:16:53:48 +0100] "POST /activiti-app/api/query/historic-task-instances?size=100000000&sort=start&order=desc&tenantId=tenant_1 HTTP/1.1" 400 510
  

• Fired that same REST call manually via Postman and a body like

  {
  "taskName":"çãçãçãçãçãçãçãçãçã"	
  }

  is working fine.

• Conclusion is, that the JSON posted from activiti-admin must be corrupted somehow