Discord4J | reactive library to enable | Bot library

I currently code a Discord bot in Java with Discord4j. Now, I want to get the mentioned user IDs (already did that) and convert them into Member object, but I don't know how to do it.

That's my code currently:

I'm packaging a shadow jar of my app. The app uses kotlin and some external dependencies. All dependencies are in my jar but i get the following exception during runtime:

java.lang.NoSuchMethodError: java.util.Optional.isEmpty()Z

The Z at the end is always there; I don't where it comes from.

I checked multiple example of build.gradle files and mine seems to be good.

(discord4j 3.1.0) So i want to get all the messages from a (Guild)MessageChannel, but as far as i know there is no straight forward way of doing it (what i mean by that there is no channel.getMessages().block() or something). What i've been using as a substitue for a while now, is a method which gets the last message of the channel, and then gets all messages before that.

I'm currently working on a bot with discord4j where I want to add a reaction(emoji) to a message. But i have no clue, how to use the addReaction() method and every example i find is using an older version. In earlier versions of dicord4j you could give a string of the unicode representation of the emoji as the parameter, but now it just takes in an object of the type ReactionEmoji. I looked at its methods nothing really makes sense except the ReactionEmoji.unicode(String raw) but then i get the error-message "unknown emoji". As input of the string i tried the unicode, the actual emoji itself, and i went into debug mode, added a reaction to a message, then took the reaction in debug mode, and copied the raw value of the reaction, pasted it as the input parameter of the unicode() mehtod , but it still didn't recognize it as an emoji. Is there some documentation i can't find? My code :