@Nullable
    public static HttpHeaders get(RequestContext ctx) {
        requireNonNull(ctx, "ctx");
        return ctx.attr(GRPC_WEB_TRAILERS);
    }
Returns the gRPC-Web trailers which was set to the specified {@link RequestContext} using
{@link #set(RequestContext, HttpHeaders)}.
core/src/main/java/com/linecorp/armeria/internal/common/InternalGrpcWebTrailers.java