Fix mail Text field not displayed in Summary tab

1. install Nuxeo IMAP Connector
2. create an EmailFolder and configure it for IMAP for example.
3. retrieve some mails by clicking Check Email
4. click on a mail title to open it
5. in the Summary tab the Text field is empty

Using Chrome Inspector the field is an iframe missing the ID in its link:

http://localhost:8080/nuxeo/restAPI/preview/default//default/?blobPostProcessing=true

Adding manually the Document ID for mail indeed shows the mail content:

http://localhost:8080/nuxeo/restAPI/preview/default/18b2083c-96cb-484c-97ca-307c1fd3c6a1/default/?blobPostProcessing=true