Bokeh Plot: glyph refers to non-existent column_name

# coding: utf-8

import math

from bokeh.io import show, output_file
from bokeh.plotting import figure
from bokeh.models import GraphRenderer, StaticLayoutProvider, Oval
from bokeh.palettes import Spectral8

N = 8
node_indices = list(range(N))

plot = figure(title="Graph Layout Demonstration", x_range=(-1.1,1.1), y_range=(-1.1,1.1),
              plot_width=250, plot_height=250,
              tools="", toolbar_location=None)

graph = GraphRenderer()

graph.node_renderer.glyph = Oval(height=0.1, width=0.2, fill_color="color")
graph.node_renderer.data_source.data = dict(
    index=node_indices,
    color=Spectral8
    )
graph.node_renderer.data_source.name = "Node Renderer"

graph.edge_renderer.data_source.data = dict(
    start=[0]*N,
    end=node_indices)
graph.edge_renderer.data_source.name = "Edge Renderer"

### start of layout code
circ = [i*2*math.pi/8 for i in node_indices]
x = [math.cos(i) for i in circ]
y = [math.sin(i) for i in circ]

graph_layout = dict(zip(node_indices, zip(x, y)))
graph.layout_provider = StaticLayoutProvider(graph_layout=graph_layout)

plot.renderers.append(graph)

#output_file("graph.html")
show(plot)