Hello, I am running Gnome Shell 48.4 but also tested this on the nightly version running v.49. When I invoke sushi to preview a file with space bar, a blue-diamond shaped icon appears in the dock:

This is a standard icon and makes me question if this is normal behavior or if the icon of the previewer should be the same of the actual file we are previewing? I wonder if I removed any necessary dependency or package.
It would be nice if, for example, when previewing an image file, the correct icon would be shown instead as the blue one looks like something is missing:

Thank you and looking forward daily driving v 49!