Bug report

Bug summary

Masked arrays are nicely supported by MPL. The masked data is not plotted and even the line interrupted.
However, when the data is str (categorical) the mask is completely ignored.

Code for reproduction

import numpy.ma
x = range(3)
y = numpy.ma.array(['hello', 'bye', 'bye2'], mask=[False, True, False])
plt.plot(x,y)
plt.show()

Actual outcome

Expected outcome

Probably the "bye" label should not even be put in the y-axis.
There should be no line but two "dots" in hello and bye2.

Matplotlib version

• Operating system: Windows
• Matplotlib version (import matplotlib; print(matplotlib.__version__)): 3.3.4
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: 3.8

Installed from conda-forge