helmsman: Variable substitution not working in env files

It seems that environment variables are not substituted in env files. I use helmsman 3.9.0. I checked the godotenv library that this project uses for loading env files and from version 1.3.0 it should work. Helmsman 3.9.0 uses 1.4.0 of this lib.

Example:

helmsman.yaml

context: mycontext
metadata:
  test: "${TEST_VAR}"

.env file

TEST_VAR=${SOMETHING}

Calling helmsman:

export SOMETHING=some_value
helmsman --debug -e .env -f helmsman.yaml

result (from helmsman output)

Metadata: 
--------- 
test :  

Context: 
--------- 
mycontext

Am I doing somethong wrong or is it a bug?