I set the value of a NBT tag with the Persistent data type "String" but when I try get the same nbt tag with the code 

 
{{ String uuids = container.get(Data.SUMMONING_MOB_UUIDS.key, PersistentDataType.STRING);}}
 
It tells me that
Caused by: java.lang.IllegalArgumentException: The found tag instance (NBTTagByte) cannot store String
 
This happens when I right click the shard item and i open the menu, click the summoning icon(s), right click with it in my hand, reload and then try right clicking again.