Avoid Null Reference in Core

[omad]

This is split from #1866. I think it somehow happened, but I don't remember the details.

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📚 Documentation preview 📚: https://opendatacube--2011.org.readthedocs.build/en/2011/

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.00%. Comparing base (082f10b) to head (5faa2ef).
⚠️ Report is 369 commits behind head on develop.

Files with missing lines	Patch %	Lines
datacube/api/core.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2011   +/-   ##
========================================
  Coverage    86.00%   86.00%           
========================================
  Files          147      147           
  Lines        16049    16051    +2     
========================================
+ Hits         13803    13805    +2     
  Misses        2246     2246           

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[SpacemanPaul]

LGTM.