fix: Sources defined empty env vars

[jasonrowsell]

Closes: #11455

[medikoo]

Thank you @jasonrowsell, it looks great!

[codecov]

Codecov Report

Base: 85.86% // Head: 85.86% // No change to project coverage 👍

Coverage data is based on head (6f15fef) compared to base (968ddd5).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 6f15fef differs from pull request most recent head 40f9236. Consider uploading reports for the commit 40f9236 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11629   +/-   ##
=======================================
  Coverage   85.86%   85.86%           
=======================================
  Files         315      315           
  Lines       13191    13191           
=======================================
  Hits        11327    11327           
  Misses       1864     1864           

Impacted Files	Coverage Δ
lib/configuration/variables/sources/env.js	100.00% <100.00%> (ø)

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[jasonrowsell]

@medikoo Ready to merge :) Hopefully the Stale PR and Issue can be closed after merging 👍