My solution is:
function out_str = cellstr_joiner(in_cell, delim)
y=in_cell;
y(find(cellfun(@isempty,cellfun(@strtrim,y,'UniformOutput',false))))=[];
out_str = strjoin(y);
out_str(find(out_str==' '))=delim;
end
On Matlab all tests pass but on the cody website the second test fail!