Fix bug in custom list sharing log line.

[dbernstein]

Partially resolves: https://ebce-lyrasis.atlassian.net/browse/PP-708

Description

Minor fix to logging line formatting: The code was hitting an unexpected NoneType and blowing up the list sharing routine.

Motivation and Context

https://ebce-lyrasis.atlassian.net/browse/PP-708

How Has This Been Tested?

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (bcdad08) 89.89% compared to head (c2b0300) 89.89%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
core/query/customlist.py	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1631   +/-   ##
=======================================
  Coverage   89.89%   89.89%           
=======================================
  Files         249      249           
  Lines       29019    29021    +2     
  Branches     6607     6608    +1     
=======================================
+ Hits        26086    26088    +2     
  Misses       1936     1936           
  Partials      997      997           

Flag	Coverage Δ
Api	75.87% <33.33%> (-0.01%)	⬇️
Core	58.57% <0.00%> (-0.01%)	⬇️
migration	26.16% <0.00%> (-0.01%)	⬇️

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[jonathangreen]

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