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: log.m
    path of file: ./repos/chebfun/@chebfun3
    
    the code of the file until where you have to start completion: function f = log(f)
%LOG   Natural logarithm of a CHEBFUN3.
%   LOG(F) is the natural logarithm of F. This function gives an error 
%   message if the function passes through or becomes numerically close to 
%   zero.
%
% See also CHEBFUN3/COMPOSE.

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

    
function f = log(f)
%LOG   Natural logarithm of a CHEBFUN3.
%   LOG(F) is the natural logarithm of F. This function gives an error 
%   message if the function passes through or becomes numerically close to 
%   zero.
%
% See also CHEBFUN3/COMPOSE.

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

% Empty check: 
if ( isempty(f) ) 
    return 
end