[Prefix Manager Fixes]

Velen/src/main/java/pw/mihou/velen/prefix/VelenPrefixManager.java

Line 124 in a605262

return prefix;

Velen/src/main/java/pw/mihou/velen/prefix/VelenPrefixManager.java

Line 92 in a605262

prefixes.put(server, prefixLoader.load(server));

All of these should check if the prefix value is null and handle it appropriately by defaulting to the default prefix, in the case of the reloadPrefix. I think I would prefer having it remove the prefix if it is null though, it's not a critical thing to change since it's still part of the end-user to ensure that the value shouldn't really be null (in my opinion).