default GrpcExceptionHandlerFunction orElse(GrpcExceptionHandlerFunction next) {
        requireNonNull(next, "next");
        if (this == next) {
            return this;
        }
        return (ctx, status, cause, metadata) -> {
            final Status newStatus = apply(ctx, status, cause, metadata);
            if (newStatus != null) {
                return newStatus;
            }
            return next.apply(ctx, status, cause, metadata);
        };
    }
Returns a {@link GrpcExceptionHandlerFunction} that returns the result of this function
when this function returns non {@code null} result, in which case the specified function isn't executed.
when this function returns {@code null}, returns a {@link GrpcExceptionHandlerFunction} that the result
of the specified {@link GrpcExceptionHandlerFunction}.
grpc/src/main/java/com/linecorp/armeria/common/grpc/GrpcExceptionHandlerFunction.java