fix: handle case where taxo cache is empty

[mmta]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 95.84%. Comparing base (eabd341) to head (f737f71).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
- Coverage   95.85%   95.84%   -0.01%     
==========================================
  Files          32       32              
  Lines        6073     6083      +10     
==========================================
+ Hits         5821     5830       +9     
- Misses        252      253       +1     

Flag	Coverage Δ
unittests	95.84% <92.85%> (-0.01%)	⬇️

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Files	Coverage Δ
server/src/manager.rs	95.20% <92.85%> (-0.09%)	⬇️