Can't convert PDF into image, because of 'no images defined' error
You are missing the optional Ghostscript dependency gs - which is not optional if you want to convert a PDF file.
If which gs doesn't resolve to the ghostscript binary (e.g. you have an alias with the same name), edit the path to Ghostscript in delegates.xml.
You can also try doing:
brew uninstall ghostscriptbrew install ghostscript
That fixed it for me.