Hiding a View if empty when contextual filter is already used
I found a very simple answer to this question.

The problem I was having was two contextual filters, Content:NID from URL, and Global:Null Hide If empty, which stopped the view displaying even if full.

Instead, I simply added a Filter Criteria for one of the fields in my view, with :fid on the end. In my case, it was Content: Sidebar Images:fid (not empty)

Now the view shows if it has content, and hides completely, including block region if empty.