Steps to Reproduce:

tag = 'non-existing-tag'
arch 'x86_64'
Run runroot(tag, arch, ['echo', 'hello', 'world'], )

Actual result:

API call doesn't return some message
Web interface returns this after the click to runroot task:

Error
An error has occurred while processing your request.
IndexError: list index out of range
Full tracebacks disabled

Expected result:

Should be returning an error message that tag is not existing and on web interface should be normal task info with the failed state.