Importing assets gives warranty error

[gitH73]

When I click import (assets), I get this error:
Warranty: validation.import_field_empty

I noticed, that warranty isn't connected with any field:

As soon as I connect it, the import is fine:

Can this (value for field warranty) be assigned automatically or can be set to unrequired?

[gitH73]

Solution: header for warranty in 'Sample asset import CSV' from your website was named 'Warranty', changing it to 'Warranty Months' helped.