iterating through g.nodes returns None eventually

(console script plugin)

I'm iterating over g.nodes and changing the color of a node according to its position

f = #scaling factor from X,Y range to RGB range
for v in g.nodes: color_node(v)

def color_node(v):
x, y = v.position
r = int(x_f)
b = int(y_f)
v.color = Color(r, 0 ,b)

it works for a few nodes until it throws an exception as NoneType has not position attribute. I don't see why it should eventually reach a None object. Data Table shows no empty rows, same iteration with only print(v) also doesn't fail. could be some concurrency related stuff.