network lint fixes

[3nprob]

Two minor non-functional changes:

• remove unused List typing import
• Use -n instead of x-hack for checking for empty var in shell script

Related

• Broken out from Add support for IPv6 Virtual DNS (#462) #592

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.10%. Comparing base (ad07468) to head (9311abb).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #594   +/-   ##
=======================================
  Coverage   71.10%   71.10%           
=======================================
  Files           3        3           
  Lines         481      481           
=======================================
  Hits          342      342           
  Misses        139      139           

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