Fix issue where the following causes obscure catalog compilation errors:
Fix issue where the following causes obscure catalog compilation errors:

```
file { '/tmp/somefile':
  ensure => 'file',
}

File['/tmp/somefile'] -> Package <| |>

ensure_packages($somearray)
```

If $somearray is undefined or one of the elements contains an empty
string, an error like the following is thrown:

Could not find resource 'Package[]' for relationship from
'File[/tmp/somefile]' on node $::fqdn

DavidS/puppetlabs-stdlib,HelenCampbell/puppetlabs-stdlib,jbondpdx/puppetlabs-stdlib,fuel-infra/puppetlabs-stdlib,puppetlabs/puppetlabs-stdlib