v2 API examples are not working

[jamesamcl]

On https://www.ebi.ac.uk/ols4/help they show 500 errors, for example the top example in the V2 property controller

{
  "status": 500,
  "message": "class java.lang.String cannot be cast to class java.util.Collection (java.lang.String and java.util.Collection are in module java.base of loader 'bootstrap')"
}