Ensure Debugger renders without error

[philippjfr]

Fixes #6416

[codecov]

Codecov Report

Attention: Patch coverage is 45.45455% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 71.62%. Comparing base (4581b4a) to head (195667b).
Report is 6 commits behind head on main.

Files	Patch %	Lines
panel/tests/ui/widgets/test_debugger.py	45.45%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6423       +/-   ##
===========================================
- Coverage   82.03%   71.62%   -10.41%     
===========================================
  Files         305      306        +1     
  Lines       45730    45741       +11     
===========================================
- Hits        37515    32764     -4751     
- Misses       8215    12977     +4762     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	71.62% <45.45%> (-0.01%)	⬇️

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