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: bramila_clusters2RGBnii.m
    path of file: ./repos/bspm/thirdparty/bramila
    
    the code of the file until where you have to start completion: function bramila_clusters2RGBnii(cfg)
%
%	cfg.infile = path to nii file

    
function bramila_clusters2RGBnii(cfg)
%
%	cfg.infile = path to nii file
%	cfg.colors = colormap file
% cfg.output_prefix= a string such './niis/modules' so that it will produce three files named ./niis/modules_R.nii ./niis/modules_G.nii ./niis/modules_B.nii
if(isfield(cfg,'output_prefix')==0)
	error('You need to specify output_prefix');
end

if(isa(cfg.output_prefix,'char')==0 || isempty(cfg.output_prefix) || strcmp(cfg.output_prefix,''))
	error('output_prefix cannot be empty and must be a string')
end



nii=load_nii(cfg.infile);
nii.img=round(nii.img);
ud=unique(nii.img);
%ud(find(ud)==0)=[];


if(any(ud<0)) error('only positive cluster IDs'); end