Description of problem:
When cloning recipe in webui with:
<hypervisor op="=" value=""/>

validation of xml fails with:

Job failed schema validation. Please confirm that you want to submit it.

    * Line 22, col 0: Did not expect element hypervisor there
    * Line 23, col 0: Element and has extra content: hypervisor
    * Line 22, col 0: Element hostRequires has extra content: and
    * Line 6, col 0: Invalid sequence in interleave
    * Line 6, col 0: Element recipe failed to validate content
    * Line 5, col 0: Element recipeSet failed to validate content

If I remove this tag, there are no warnings.

How reproducible:
100%

Steps to Reproduce:
1. clone this recipe: 
https://beaker.engineering.redhat.com/jobs/clone?job_id=118956

Actual results:
validation fails (see above)

Expected results:
recipe should be accepted without warnings/errors

Additional info: