The dashboard_url field must return a string value instead of a field

[JCL38-ORANGE]

With recent versions of cloudfoundry the null value is not more allowed for the dashboard_url field.
This problem appears with the bump of capi-version 1.61 (https://bosh.io/releases/github.com/cloudfoundry/capi-release?version=1.61.0)
The problem is referenced there :

• https://www.pivotaltracker.com/n/projects/2105761/stories/157601813
• https://github.com/openservicebrokerapi/servicebroker/pull/437/files
  The broker code must be updated to return an empty string instead of a null value for dashboard_url field.

[JCL38-ORANGE]

Some additional information :
When the service creation is asked via the CF CLI : cf cs
The following error is raised by the CC :
ECHEC
Erreur de serveur, code de statut : 502, code d'erreur : 10001, message : The service broker returned an invalid response for the request to <redacted_request> :
The property '#/dashboard_url' of type null did not match the following type: string

[JCL38-ORANGE]

Fix with 69e6a26