metadataFor("non-existing-bucket") should resolve with undefined

[lukemelia]

Currently metadataFor("non-existing-bucket") throws an error in the card if "non-existing-bucket" is not defined:

TypeError: Cannot call method 'call' of undefined
    at Object.Conductor.metadataConsumer.options.requests.metadataFor

I think this scenario should resolve with undefined instead.

[lukemelia]

Same thing goes if the metadata property is not defined on the card.