You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: bb_square.m
    path of file: ./repos/OpenTLD/bbox
    
    the code of the file until where you have to start completion: % Copyright 2011 Zdenek Kalal
%
% This file is part of TLD.
% 
% TLD is free 
    
function bb2 = bb_square(bb1)
% Makes all bboxes square with the same area.

if isempty(bb1);
    bb2 = [];
    return;
end