Hiera 3 + Puppet 4.2 can't manage empty value in yaml datasource - puppet

Question

I'm facing some issues to use Hiera 3 with Puppet 4.2.
When applying my puppet manifest using this command:
puppet apply environments/production/manifests/init.pp --hiera_config=hiera.yaml
I get the following error:
Error: Evaluation Error: Error while evaluating a Function Call, Could not find data item myclass::ensure in any Hiera data file and no default supplied at /home/vagrant/temp/environments/production/manifests/init.pp:13:39 on node a
Here is the directory structure :
$ tree
.
├── environments
│   └── production
│   ├── config.yaml
│   └── manifests
│   └── init.pp
└── hiera.yaml
content of config.yaml:
$ cat hiera.yaml
---
:backends:
- yaml
:hierarchy:
- config
:yaml:
:datadir: environments/production
content of init.pp:
class myclass(
$version = $myclass::params::version,
$ensure = $myclass::params::ensure,
) inherits myclass::params {
notify {"$version": }
notify {"$ensure": }
}
class myclass::params {
$version = hiera('myclass::version', '1.0.0')
$ensure = hiera('myclass::ensure', 'running')
}
class {'myclass': }
content of hiera data source:
$ cat config.yaml
---
myclass::version: '1.0.0'
myclass::ensure:
Looks like Hiera can't handle empty values from a yaml data source and/or replace them by default value?