public PathStreamMessageBuilder alloc(ByteBufAllocator alloc) {
        requireNonNull(alloc, "alloc");
        this.alloc = alloc;
        return this;
    }
Sets the specified {@link ByteBufAllocator}.
If unspecified, {@link ByteBufAllocator#DEFAULT} is used by default.
core/src/main/java/com/linecorp/armeria/common/stream/PathStreamMessageBuilder.java