Treat blank environment variables as nil

[yasseur1007]

Consider blank variables as nil.

Useful when using "${ENV_VARIABLE}" way during the compile time, that is converted to "" when no env found at run time.

[romul]

Hello, @yasseur1007! This is your first Pull Request that will be reviewed by Ebert, an automatic Code Review service. It will leave comments on this diff with potential issues and style violations found in the code as you push new commits. You can also see all the issues found on this Pull Request on its review page. Please check our documentation for more information.

[romul]

Ebert has finished reviewing this Pull Request and has found:

• 1 possible new issue (including those that may have been commented here).

You can see more details about this review at https://ebertapp.io/github/romul/newrelic.ex/pulls/9.

[yasseur1007]

hi @romul can you have a look at this PR?
also i'm not sure the Ebert issue found is related to the changes i've made :)

[sb8244]

Hi @yasseur1007. This is an old PR, but I'm wondering if you still need this functionality? If so, we can look at adding it in.