* Fix: Handle empty nested keys on YAML provisioning datasources

As we provision a datasource via a YAML file, we attempt to transform the
file into sensible Go types that the provisioning code can use.

While this happens, there is a chance some of the keys nested within
the YAML array are empty.

This fix allows the YAML parser to handle empty keys by null checking
the return of `reflect.TypeOf` which according to the documentation:

> TypeOf returns the reflection Type that represents the dynamic type of i. If i is a nil interface value, TypeOf returns nil.

Can return nil.

* Add tests