private DeploymentSpec.RevisionTarget readRevisionTarget(String revision) {
        return switch (revision) {
            case "next" -> RevisionTarget.next;
            case "latest" -> RevisionTarget.latest;
            default -> throw new IllegalArgumentException("Illegal upgrade revision target '" + revision + "': " +
                                                          "Must be one of 'next', 'latest'");
        };
    }
Returns true if the given value is "true", or if it is missing
config-model-api/src/main/java/com/yahoo/config/application/api/xml/DeploymentSpecXmlReader.java