Fix: image_detector skip None values in casted_versions

[benieric]

Issue #, if available:

Description of changes:

• Filter None values in casted_versions tuple
• Fix bug introduced in image_detector from latest_image utility in image_uris.retrieve - previously if one of the casted_version values was None this method would throw an Error. New functionality in image_uris.retrieve causes this to return latest image version even when the casted_versions contains a more appropriate version

Testing done:

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