Steps to reproduce:

1. Set an environment variable in global configuration for example GIT_URL=https://some/url/$PROJECT

2. Set parameter of PROJECT=netvirt for example
3. Create a job that calls "inject" setting a different parameter for example "VAR=123" and then in a shell step immediately after "echo $GIT_URL".

4. Run job

Issue:

GIT_URL is overrided by inject to be a literal string of '$GIT_URL/netvirt/netvirt/netvirt/netvirt'

Expected result:

The inject plugin should not be overriding existing variables that are not passed in during the inject call.