Bug report

Bug summary

When giving the variable None to the label argument of matplotlib.pyplot.colorbar(), i.e label=None, the label still appears, with the text "None", as if being given label="None".

Code for reproduction

import numpy as np 
import matplotlib.pyplot as plt 

fig, ax = plt.subplots() 
img = ax.imshow(np.random.random((10,10))) 
fig.colorbar(mappable=img, ax=ax, label=None)   
fig.show()

Actual outcome

Expected outcome

The label should not appear. The bug is still present in matplotlib 3.1.

Matplotlib version

• Operating system: Ubuntu 18.04.2 LTS x86_64
• Matplotlib version: 2.2.3
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: 3.7.2
• Jupyter version (if applicable):
• Other libraries:

I installed matplotlib via conda through the default channel.