How to implement not with if statement in Ember Handlebars?

Question

I have a statement like this:

{{#if IsValid}}

I want to know how I can use a negative if statement that would look like that:

Answer 1

{{#if items.length}}
    //Render
{{/if}}

Here items.length .. if it returns some value except null, then only it will enters into the if loop.

NOTE : You can check Boolean values also. In If block

{{#if booleanFloag}}