Issue with json deserialiser. Due to recent Mojang change https://minecraft.gamepedia.com/Raw_JSON_text_format for json format deprecating "value" and replacing it with "contents" we have issue where minecraft code converts json correctly and replaces everything to how it should look like, while md_5.bungee.chat parser will still try to look up for "value" section which no longer exists and will throw out error. Something like

[00:25:31 WARN]: java.lang.NullPointerException
[00:25:31 WARN]:        at net.md_5.bungee.chat.ComponentSerializer.toString(ComponentSerializer.java:58)

This is clearly visible as an issue in net.md_5.bungee.chat.BaseComponentSerializer class, as its still tries to look up for the old value and failing while doing so.