Pre release fixes for v0.31.0

[AdeelH]

Overview

This PR

• fixes bugs discovered during testing for the 0.31.0 release
• updates tutorial notebooks
• makes some other minor changes (see commits)

Checklist

• Added unit tests, if applicable
• Updated documentation, if applicable
• Added needs-backport label if the change should be back-ported to the previous release
• PR has a name that won't get you publicly shamed for vagueness

Notes

Eval comparison with previous release.

(The null class was removed.)

(The null class was removed.)

f-61b3-4232-912a-9f3ee8d3ce83)

Testing Instructions

• Ensure docs build looks fine.

---

Closes #2213
Closes #2214

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.34%. Comparing base (0f45c2c) to head (5fc3634).
Report is 27 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2215   +/-   ##
=======================================
  Coverage   90.34%   90.34%           
=======================================
  Files         199      199           
  Lines        9908     9910    +2     
=======================================
+ Hits         8951     8953    +2     
  Misses        957      957           

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