Description

The checkpoint CIS-DI-0010 is raising a FATAL error even when the detected environment variable is empty.

It is actually a common practice to have empty environment variable, in order to "document" them.

Example: ENV POSTGRES_PASSWORD=

If dockle can read the environment variable value, it would be great if it would not report in case the variable is empty.

How to reproduce

My Dockerfile:

FROM alpine:latest

ENV APPLE_SAUCE_SECRET=

The result:

FATAL	- CIS-DI-0010: Do not store credential in environment variables/files
	* Suspicious ENV key found : APPLE_SAUCE_SECRET (You can suppress it with --accept-key)

I can indeed suppress the error but I think this should not be reported as a non-compliance.