If I have the following data:

data <- list(users = list(list(name = "bob"), list(name = "alice")))

I might want to know if the list is empty or not. For example, this would be my desired template:

template <- "{{#users.length}}Users: {{#users}}{{name}} {{/users}}{{/users.length}}{{^users.length}}No users{{/users.length}}"

It uses .length as a conditional that is true if there are any elements and false if it's empty.

This is not an official standard mustache feature, but it is implemented in some languages. See here for details.