global.json defines "image" property, so you can't unset it

[Faldrian]

Describe the bug
You can't generate a documentation with the default theme and not have an "HomepageImage" on the global landing page.

To Reproduce
Steps to reproduce the behavior:

1. create a new project with an index.md and another Markdown file (so generation works)
2. Create a global.json file next to it and define title and author. No "image" is defined.
3. The generated documentation will habe an image with «src=""» embedded, resulting in alt-text shown.

Expected behavior
If "image" would not be defined, you can leave it blank and the template logic of "hasImage" would work.

Additional context
This is a minor thing... but causes me to use my own template or a blank image, which is not ideal. ^^

[onigoetz]

Hi, I made a fix in the master branch, you can try to take the project from dev-master or the latest docker image, I'll release the fix soon

[onigoetz]

Hi, this has been released in Version 0.14.0