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: meanNN.m
    path of file: ./repos/Gaussian-Process-Regression/gpml-matlab-v4.2-2018-06-11/mean
    
    the code of the file until where you have to start completion: function [m,dm] = meanNN(c,v, hyp, x)

% Nearest neighbor mean function. The mean function is parameterized as:
%

    
function [m,dm] = meanNN(c,v, hyp, x)

% Nearest neighbor mean function. The mean function is parameterized as:
%
% m(z) = v_j, j = arg min_i d(ci,x) where d is the Euclidean distance and ci is
%                                   the ith cluster center.
%
% The hyperparameters are:
%
% hyp = [ ]
%
% Copyright (c) by Hannes Nickisch, 2016-04-16.
%
% See also MEANFUNCTIONS.M.

if nargin<4, m = '0'; return; end