graph_tool bugg, can't use vertex_average on an empty graph.

gistfile1.txt

...........................................................................
/home/fer/miniconda3/lib/python3.5/site-packages/graph_tool/stats/__init__.py in vertex_average(g=<GraphView object, undirected, with 0 vertices a...Graph 0x7f5f5a9be400, at 0x7f5f5a9bef28>, False)>, deg='total')
    241     try:
    242         a = array(a.a)
    243         aa = array(aa.a)
    244     except AttributeError:
    245         pass
--> 246     a /= count
        a = 0.0
        count = 0
    247     aa = sqrt((aa / count - a ** 2) / count)
    248     return a, aa
    249 
    250 

ZeroDivisionError: float division by zero
___________________________________________________________________________