Can Data expectations be set to WARN instead of FAIL?

Some values in a column I have can be NULL for various business reasons. Is there a way for me to set data expectations so that they only WARN when NULLs are detected, instead of failing the entire expectation?

As mentioned in the getting started on data expectations part of our documentation (https://www.palantir.com/docs/foundry/transforms-python/data-expectations-getting-started/#create-checks), the check can be set to WARN or FAIL when the error occurs like so

Check(expectation, 'Check unique name', on_error='WARN/FAIL')