Fixed java ver method

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/command/Command.java

@@ -79,7 +79,7 @@ public abstract class Command {
      * @return true if they can use it, otherwise false
      */
     public boolean testPermission(CommandSender target) {
-        if ((permission == null) || (permission.isEmpty()) || (target.hasPermission(permission))) {
+        if ((permission == null) || (permission.length() == 0) || (target.hasPermission(permission))) {
             return true;
         }