default RequestLogLevelMapper orElse(RequestLogLevelMapper other) {
        requireNonNull(other, "other");
        if (this == other) {
            return this;
        }
        return log -> {
            final LogLevel logLevel = apply(log);
            if (logLevel != null) {
                return logLevel;
            }
            return other.apply(log);
        };
    }
Returns a composed {@link RequestLogLevelMapper} which represents a logical OR of this
{@link RequestLogLevelMapper} and the given {@code other}.
If this {@link RequestLogLevelMapper#apply(RequestOnlyLog)} returns {@code null}, then the other
{@link RequestLogLevelMapper} will be applied.
core/src/main/java/com/linecorp/armeria/common/logging/RequestLogLevelMapper.java