Conditionals - If a field is not available

Is there a way to test if a field is not available? Basically the negated version of {{#field}}{{/field}}
My use case is that I have two fields: {{main}} and {{fallback}}
They both represent roughly the same information, but {{main}} contains a bit more stuff, so it’s preferable to use that if it’s available.
The problem is that {{main}} is not always available, while {{fallback}} is guaranteed to always be available.
Right now I can do this:


But this will show nothing if the main field is not available.
So how do I show {{fallback}} in the case that {{main}} is not available?

Figured it out, the syntax is: