I found that MAVEN_REPO_URL is mandatory in some KIE server templates. In reality, when one sets them up to work with a BC built-in repo, the Maven repo URL is taken from BUSINESS_CENTRAL_SERVICE and so MAVEN_REPO_URL is not needed. The documentation already instructs the user to configure one or the other, for example: https://access.redhat.com/documentation/en-us/red_hat_decision_manager/7.7/html/deploying_a_red_hat_decision_manager_authoring_or_managed_server_environment_on_red_hat_openshift_container_platform/environment-authoring-con#template-deploy-connectcentral-additional-server-managed-proc

(CREDENTIALS_SECRET is described above in teh same doc, as one has to set up CREDENTIAL_SECRET in all cases anyway)