WARN No fields selected, won't update anything

All,

trying to change the formatter of one of our devices using the CLI (can’t get to the Web based console for now). I get:

$ ttn-lw-cli end-devices set my-application-id my-dev-id --formatters.up-formatter-parameter-local-file formatter.js
WARN	No fields selected, won't update anything

I have seen a few references to this “warning” but no solution. I have tried other tags that would change something, getting the same warning.

Any ideas?