MATLAB: How to concatenate different cells of a cell array in one cell without a loup ?

cell arraysMATLAB

this is my cell B

B =

    {1x2 cell}    {1x3 cell}
How to transorm it into {1x5 cell} 
???

B = {{magic(2) magic(2)},{magic(2) magic(2) magic(2)}}
B2 = cat(2,B{:})

Cell_array = {1,[],magic(2);'stirng',[],[]}
cellfun('isempty',Cell_array)

a={'kkk', 'lll', 'xxx', 'jjj.xls'}';
out = [a(:)';repmat({'_'},1,numel(a))];
out = [out{:}];
out = out(1:end-1);

variant 2

out = cell(1,2*numel(a)-1);
out(1:2:end) = a;
out(2:2:end) = {'_'};
out = [out{:}];