Adds protection around nulls. (#361)

Author: tastybento

src/main/java/world/bentobox/challenges/commands/admin/ChallengesAdminCommand.java

@@ -63,6 +63,7 @@ public boolean execute(User user, String label, List<String> args)
 
             return true;
         }
+        this.showHelp(this, user);
         return false;
     }
 }

src/main/java/world/bentobox/challenges/database/object/ChallengeLevel.java

@@ -153,6 +153,9 @@ public String getFriendlyName()
      */
     public ItemStack getIcon()
     {
+        if (icon == null) {
+            icon = new ItemStack(Material.PAPER);
+        }
         return icon.clone();
     }