Fix environment variable merging to allow empty string values

[k44]

This pull request fixes the logic in mergeSafeChainProxyEnvironmentVariables to ensure that environment variables with empty string values are correctly copied.
A corresponding test has been added to verify this behavior.

• Fixes an issue where empty string values were previously ignored
• Adds a unit test to cover this case

Summary by Aikido

Security Issues: 0	Quality Issues: 0	Resolved Issues: 0

🐛 Bugfixes

• Allowed empty string environment variables to be preserved during merge

^{More info}