In php, should I return false, null, or an empty array in a method that would usually return an array?

I've found several responses to this, but none pertaining to PHP (which is an extremely weak typed language):

With regards to PHP, is it appropriate to return false, null, or an empty array in a method that would usually return an array, but has a failure occur?

In other words, if another developer jumped in on my project, what would they expect to see?