If empty deny list allow storing

[hardillb]

fixes #3188

Description

Unable to clear the Prevent Install of External nodes section of the Palette Settings.

Related Issue(s)

#3188

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Backport needed? -> add the backport label
• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

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

Comparison is base (4b355e1) 40.41% compared to head (35d1862) 40.41%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
forge/db/controllers/ProjectTemplate.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3232      +/-   ##
==========================================
- Coverage   40.41%   40.41%   -0.01%     
==========================================
  Files         587      587              
  Lines       21544    21546       +2     
  Branches     5176     5177       +1     
==========================================
  Hits         8707     8707              
- Misses      12837    12839       +2     

Flag	Coverage Δ
backend	76.83% <0.00%> (-0.01%)	⬇️
frontend	1.95% <0.00%> (-0.01%)	⬇️

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