1. All '*.env' files in an 'environment.d' directory alongside each
potential 'environment' file will be parsed and added to the
environment.
2. For the purposes of configuration merging, an environment definition
exists at one level if either the 'environment' file is defined or
its corresponding 'environment.d' contains any valid '*.env' file.
3. Variable declarations of the form "VARIABLE=", with no following
value, will be written to the environment as empty strings.
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