cyberdudedk/Bukkit — comment on commit 5dc0ac1c54b4183333d615125d837565c7a6ee37
File: src/main/java/org/bukkit/util/metadata/MetadataNode.java line 20
By ZachBora:

In my opinion it should at least allow List or HashMaps of String and other simple types. And not allow objects like Player... not sure if it can be possible?