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: sum.m
    path of file: ./repos/chebfun/@chebfun3
    
    the code of the file until where you have to start completion: function g = sum(f, dim)
%SUM   Definite integration of a CHEBFUN3 in one variable.
%   G = sum(F, DIM) returns a CHEBFUN2 that represents the definite integral
%   of a CHEBFUN3 object F along the variable specified in DIM. DIM should
%   be 1, 2 or 3 to integrate over X, Y or Z, respectively.
%
%   G = sum(F) is the same as sum(F, 1).

    
function g = sum(f, dim)
%SUM   Definite integration of a CHEBFUN3 in one variable.
%   G = sum(F, DIM) returns a CHEBFUN2 that represents the definite integral
%   of a CHEBFUN3 object F along the variable specified in DIM. DIM should
%   be 1, 2 or 3 to integrate over X, Y or Z, respectively.
%
%   G = sum(F) is the same as sum(F, 1).
%
% See also CHEBFUN3/SUM2, CHEBFUN3/SUM3, CHEBFUN3/CUMSUM, CHEBFUN3/CUMSUM2 
% and CHEBFUN3/CUMSUM3.

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

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