3.1.2 bugfixes (see long description)

- add messages in /rank and /rankup for when the configuration has a rankup to a non-existent rank.
- add invalid rankup message
- fix error for placeholders when prestiging is disabled
- add message for when a rank has no requirements

src/main/java/sh/okx/rankup/messages/Message.java

@@ -27,7 +27,8 @@ public enum Message {
   NOT_HIGH_ENOUGH("not-high-enough"),
   PRESTIGE_SUCCESS_PUBLIC("prestige.success-public"),
   PRESTIGE_SUCCESS_PRIVATE("prestige.success-private"),
-  PRESTIGE_CONFIRMATION("prestige.confirmation");
+  PRESTIGE_CONFIRMATION("prestige.confirmation"),
+  INVALID_RANKUP("invalid-rankup");
 
   @Getter
   private final String name;