Automation operation 'WebUI.DownloadFile' builds a malformed download URL

Which prevents the blob download. See the double slash before nxbigblob in http://localhost:8080/nuxeo//nxbigblob/45436203-4d9f-4723-b071-b7a13166b28e
Debugging shows that BaseURL.getBaseURL() in operation's class DownloadFile returns http://localhost:8080/nuxeo/ (with trailing slash).

How to reproduce:

• create a user action for document type File running the following automation chain:

  - Context.FetchDocument
  - Document.GetBlob: {}
  - WebUI.DownloadFile