Images dont get rendered if the "alt text" input is an empty string

If an image is created and an empty string wired to the "Alt text" input, the image is not rendered by asciidoctor. This appears to be related to not creating the [] after the image:

image::{imgpath}[alt-text]

if alt text is an empty string, the "render.vi" for image class creates the output as:

image::{imgpath}

and this fails to render the image (at least using the pdf backend in asciidoctor)