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: ft_fetch_vol.m
    path of file: ./repos/malini/Codes/deconvolution - model/spm8/external/fieldtrip/private
    
    the code of the file until where you have to start completion: function [vol] = ft_fetch_vol(cfg, data)

% FT_FETCH_VOL mimics the behaviour of FT_READ_VOL, but for a FieldTrip
% data structure or a FieldTrip configuration instead of a file on disk.
%
% Use as
%   [vol] = ft_fetch_vol(cfg, data)
% where either of the two input arguments may be empty.
%
% The volume conductor definitions are specified in the configuration or
% data. The sensor configuration can be passed into this function in three ways:
%  (1) in a file whose name is passed in a configuration field.
%  (2) in a configuration field,
%  (3) in a data field.
% 
% % You should specify the volume conductor model with
%   cfg.hdmfile       = string, file containing the volume conduction model
% or alternatively
%   cfg.vol           = structure with volume conduction model
%   data.vol          = structure with volume conduction model
%
% See also FT_READ_VOL, FT_FETCH_DATA

% Copyright (C) 2011, Jörn M. Horschig
%
% This file is part of FieldTrip, see http://www.ru.nl/neuroimaging/fieldtrip
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%

    
function [vol] = ft_fetch_vol(cfg, data)

% FT_FETCH_VOL mimics the behaviour of FT_READ_VOL, but for a FieldTrip
% data structure or a FieldTrip configuration instead of a file on disk.
%
% Use as
%   [vol] = ft_fetch_vol(cfg, data)
% where either of the two input arguments may be empty.
%
% The volume conductor definitions are specified in the configuration or
% data. The sensor configuration can be passed into this function in three ways:
%  (1) in a file whose name is passed in a configuration field.
%  (2) in a configuration field,
%  (3) in a data field.
% 
% % You should specify the volume conductor model with
%   cfg.hdmfile       = string, file containing the volume conduction model
% or alternatively
%   cfg.vol           = structure with volume conduction model
%   data.vol          = structure with volume conduction model
%
% See also FT_READ_VOL, FT_FETCH_DATA

% Copyright (C) 2011, Jörn M. Horschig
%
% This file is part of FieldTrip, see http://www.ru.nl/neuroimaging/fieldtrip
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.
%
% $Id: ft_fetch_vol.m 7123 2012-12-06 21:21:38Z roboos $

% check input arguments
if nargin > 1 && ~isempty(data)
  data = ft_checkdata(data);
else
  data = struct; % initialize as empty struct
end