GAE app.yaml: How to set env variable that contains periods?

[Dzmitry Lazerka via StackOverflow]

I'm checking out GAE Managed VMs using app.yaml, as described here https://cloud.google.com/appengine/docs/managed-vms/java/configuring-your-app-with-app-yaml

When I do

env_variables:
  java.util.logging.config.file: 'WEB-INF/logging.properties'

I get exception

google.appengine.api.yaml_errors.EventError: Value 'java.util.logging.config.file' for key in EnvironmentVariables does not match expression '^(?:[a-zA-Z_][a-zA-Z0-9_]*)$'

Is there any way to specify custom logging.properties through app.yaml?

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