Empty environment variables create invalid compose file

[ChristianLempa]

Description:
If you add environment variables with blank input, it creates an invalid compose file filing "!!null '':" to the environment section. To fix this delete blank fields in "environment" tab.

Steps to reproduce:

1. Create a new service object
2. Edit service settings
3. Click on "environment" tab
4. Click on add with blank values
5. Close the service object

Screenshots:

[corpulent]

@xcad2k Thanks for pointing this out. I deployed a quick fix for now, but will think of a better UX for this.

[corpulent]

There is a warning now for empty environment variable keys.