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: jacobian.m
    path of file: ./repos/chebfun/@chebfun2
    
    the code of the file until where you have to start completion: function J = jacobian( f, g )
%JACOBIAN   Jacobian determinant of two CHEBFUN2.

    
function J = jacobian( f, g )
%JACOBIAN   Jacobian determinant of two CHEBFUN2.
%   J = JACOBIAN(F,G) returns the Jacobian determinant of the Jacobian matrix.
%
%   Note we return the determinant of the Jacobian matrix and not the Jacobian
%   matrix itself.
%
% See also CHEBFUN2V/JACOBIAN. 

% Copyright 2017 by The University of Oxford and The Chebfun Developers.
% See http://www.chebfun.org/ for Chebfun information.

% Empty check: 
if ( isempty( f ) || isempty( g ) )  
    J = []; 
    return
end