Environment variable VIRTUAL_ENV not passed to container

Open Source Projects Compose
1

Given this docker-compose.yml which is supposed to print the value of the container’s environment variables containing VIRTUAL_ENV:

version: '3.8'

services:
  test:
    image: alpine
    environment:
      - VIRTUAL_ENV2
      - VIRTUAL_ENV1
      - VIRTUAL_ENV
    command: sh -c 'env | grep VIRTUAL_ENV'

This is the output I receive:

> env VIRTUAL_ENV=foo VIRTUAL_ENV1=foo VIRTUAL_ENV2=foo docker-compose run --rm test

Creating test_run ... done
VIRTUAL_ENV1=foo
VIRTUAL_ENV2=foo

Environment variable VIRTUAL_ENV is missing. Why is that?