Custom visual drill down in multiple roles

Hi,

I have modified the Flow Map custom visual  from Weiweicui to see if I can make aggregations work in a hierarchy, so a user can drill down/up from a location to country, region, etc in the same chart. The flow map build the lines from a source and destination, that is, two roles. I want the users to be able to drill down in using both, so a user can see a flow for example from a Country to a Port, and rill down to see from a Port to Port, or Country to Country, etc.

I edited the capabilities.json and added the following:

    "drilldown": {

        "roles": ["Origin", "Dest"]

    },

The chart now shows a new widget like below and seems to work fine. The only problem is that the names in the dropdowns don’t appear. I expect these to be Origin and  Destination, but instead they are ‘undefined’

See below:

Can you think of where I look into to fix this. I tried finding documentation about this widget but could not find.

Thanks,

Alexis