Fix(cv_facts_v3): Handle stale and empty devices in the inventory having an image bundle of type None

[colinmacgiolla]

Change Summary

As described in issue #568 if the API call to get_device_image_info() returns type None we weren't handling this correctly

Related Issue(s)

Fixes #568

Component(s) name

arista.cvp.cv_facts_v3

Proposed changes

Check for returned type being None and handle it

How to test

Tested fix against production system running 2021.2.1 where this was first encountered. Fix resolved the problem. Issue #568 shows (with the serial number scrubbed) the cvprac API output that triggered this issue.

Checklist

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