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: undo_mask.m
    path of file: ./repos/BrainStat/brainstat_matlab/+brainstat_utils
    
    the code of the file until where you have to start completion: function Y2 = undo_mask(Y, mask, varargin)
% UNDO_MASK     Restores masked data to its original dimensions. Y2 =

    
function Y2 = undo_mask(Y, mask, varargin)
% UNDO_MASK     Restores masked data to its original dimensions. Y2 =
%   UNDO_MASK(Y, mask) restores masked data Y to its original dimension by
%   adding rows. Data that was masked out is filled with nans.
%   
%   Y2 = UNDO_MASK(Y, mask, 'axis', dim) acts along the specified dimension.
%   Defaults to 1. 
%
%   Y2 = UNDO_MASK(Y, mask, 'missing_value', val) fills missing values with 
%   the specified values. Defaults to nan.

p = inputParser;
p.addParameter('axis', 1, @isscalar);
p.addParameter('missing_value', nan, @isscalar);
p.parse(varargin{:});

new_dims = size(Y);
new_dims(p.Results.axis) = numel(mask);
Y2 = ones(new_dims) * p.Results.missing_value;

S.subs = repmat({':'},1,ndims(Y2));
S.subs{p.Results.axis} = mask; 
S.type = '()';
Y2 = subsasgn(Y2,S,Y);
end