public static void error(final Logger logger, final Throwable throwable) {
        if (throwable != null) {
            error(logger, getMessage(throwable), throwable);
        }
    }
Log Error.

@param logger    the logger
@param throwable the throwable
core/cas-server-core-util-api/src/main/java/org/apereo/cas/util/LoggingUtils.java