nightshade() on Robinson Projection and lon_0=-180

Start at the Basemap.nightshade() entry point and reproduce the example with a Robinson projection centered at lon_0=-180. Compare the shading and non-monotonic-x warning with the same example using another central longitude, and use shiftgrid and examples/contour_demo.py as the referenced context. Done means the reported projection produces correct night shading without the unexpected contour warning.

Hello! I'm plotting day/night shading on a Robinson projection centered at -180 degrees with nightshade(), and as you can see, the shading doesn't look right. I'm also getting a warning about a non-monotonically increasing x coordinate. Presumably, nightshade() is plotting a transparent contour under the hood, but I couldn't see a way to change the starting longitude in the documentation. I'm not familiar enough with Basemap to know if this is a bug or if I'm missing something. Any suggestions would be greatly appreciated!

Plot

Warning

WARNING: x coordinate not montonically increasing - contour plot may not be what you expect. If it looks odd, your can either adjust the map projection region to be consistent with your data, or (if your data is on a global lat/lon grid) use the shiftgrid function to adjust the data to be consistent with the map projection region (see examples/contour_demo.py).

Code for reproduction

from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt
from datetime import datetime
# lon_0 is central longitude of projection.
# resolution = 'c' means use crude resolution coastlines.
m = Basemap(projection='robin',lon_0=-180,resolution='c')
m.drawcoastlines()
m.fillcontinents(color='coral',lake_color='aqua')
# draw parallels and meridians.
m.drawparallels(np.arange(-90.,120.,30.))
m.drawmeridians(np.arange(0.,360.,60.))
m.drawmapboundary(fill_color='aqua')
date = datetime(2024,10,10,6)
m.nightshade(date,alpha=0.2)
plt.title("Robinson Projection")
plt.savefig('test.png')

Environment
Ubuntu and RHEL
Python 3.8.13

Please let me know if I should be providing more details