Return the Number 1 if {expr} is empty, zero otherwise.

• A List or Dictionary is empty when it does not have any items.
• A String is empty when its length is zero.
• A Number and Float are empty when their value is zero.
• v:false, v:none and v:null are empty, v:true is not.
• A Job is empty when it failed to start.
• A Channel is empty when it is closed.
• A Blob is empty when its length is zero.

For a long List this is much faster than comparing the length with zero.

Can also be used as a method:

mylist->empty()