convhull empty option (default) problems

Hello,

I have been usgin the function convhulln quite extensively and I came accross this problem recently for which I could not find any solution yet.

Consider the set of points of a cube in 3d:

x3=[0 0 0];
x4=[0 0 4];
x5=[0 4 0];
x6=[4 0 0];
x7=[4 4 0];
x8=[4 4 4];
x9=[0 4 4];

cu=[x3; x4; x5; x6; x7; x8; x9; x10];

When I try to apply convhulln with the default options disabled, as specified here:
http://fr.mathworks.com/help/matlab/ref/convhulln.html

X=convhulln(cu,{''});

i get the following error:

Error using qhullmx
Index out of bounds.

Error in convhulln (line 64)
[k,vv] = qhullmx(x', opt);

Error in main (line 40)
X=convhulln(cu,{''});
 
And I can't really seem to find the reason.

Any help is welcome

Thank you

G.