hvplot.networkx.draw fails with unsigned dtypes

[stuarteberg]

The following code can draw a networkx graph:

import numpy as np
import networkx as nx
import hvplot.networkx as hvnx

edges = np.array([[1,2],[2,3]])
g = nx.Graph()
g.add_edges_from(edges)
hvnx.draw_networkx(g)

But if you use an unsigned dtype, like this:

edges = np.array([[1,2],[2,3]], dtype=np.uint8)

...then you get an exception whose traceback ends with:

/miniforge/envs/flyem37/lib/python3.7/site-packages/holoviews/plotting/bokeh/graphs.py in <listcomp>(.0)
    220             start, end = start.astype(np.int32), end.astype(np.int32)
    221         elif nodes.dtype.kind != 'i':
--> 222             start = np.array([node_indices.get(x, nan_node) for x in start], dtype=np.int32)
    223             end = np.array([node_indices.get(y, nan_node) for y in end], dtype=np.int32)
    224         path_data = dict(start=start, end=end)

NameError: free variable 'node_indices' referenced before assignment in enclosing scope

Environment details

$ conda list | grep -E 'holoviews|hvplot|networkx|numpy|python|bokeh|matplotlib'
bokeh                     1.2.0                    py37_0    conda-forge
holoviews                 1.12.3                     py_2    conda-forge
hvplot                    0.4.0                      py_1    conda-forge
ipython                   7.5.0            py37h24bf2e0_0    conda-forge
ipython_genutils          0.2.0                      py_1    conda-forge
matplotlib-base           3.1.0            py37hfd891ef_1    conda-forge
msgpack-python            0.6.1            py37h6bb024c_0    conda-forge
networkx                  2.3                        py_0    conda-forge
neuprint-python           0.1.2                      py_0    flyem-forge
numpy                     1.16.4           py37h95a1406_0    conda-forge
python                    3.7.3                h5b0a415_0    conda-forge
python-dateutil           2.8.0                      py_0    conda-forge
python-snappy             0.5.4            py37hee44bf9_0    conda-forge

[stuarteberg]

Should be fixed when holoviz/holoviews#3773 is merged.