ignore env var set to empty string

[adhami3310]

fix #5138 even more

[codspeed-hq]

CodSpeed Performance Report

Merging #5167 will degrade performances by 4.73%

_{Comparing ignore-env-var-set-to-empty-string (88fb030) with main (3bcf01d)}

Summary

❌ 2 regressions
✅ 10 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	test_evaluate_page[_complicated_page]	62.4 ms	64.4 ms	-3.13%
❌	test_evaluate_page[_simple_page]	827 µs	868.1 µs	-4.73%