In a PureScript buffer, I run M-x psci and an empty “psci” buffer opens. Then the entry “psci/--project-root!: Wrong type argument: stringp, nil” is added to “Messages”. debug-on-error is enabled, but I don’t end up in the debugger for some reason.

It looks like psci/--project-root! doesn’t try to do anything (even report a better error, like “need a .psci file”) if locate-dominating-file returns nil.