Fixes bug in parsing report from agent versions ~> 2.6

Without this patch, puppet dashboard workers cannot parse reports from old agents (e.g.: Debian Squeeze's Version 2.6.2-5+squeeze9).

I got this error in form the workers 
```
Worker(delayed_job host:admin1 pid:9870)] Class#create_from_yaml failed with NoMethodError: undefined method `>=' for nil:NilClass
```

With the fix from this PR everything is working fine

[Compare puppet-dasboard-wip Issue #18](https://github.com/sodabrew/puppet-dashboard-wip/issues/18)