There is no usage of this method in which "all" will not cause NPE's

src/main/java/com/gmail/nossr50/util/commands/CommandUtils.java

@@ -134,7 +134,7 @@ public final class CommandUtils {
     }
 
     public static boolean isInvalidSkill(CommandSender sender, String skillName) {
-        if (skillName.equalsIgnoreCase("all") || SkillUtils.isSkill(skillName)) {
+        if (SkillUtils.isSkill(skillName)) {
             return false;
         }