Fix #857

Essentials/src/com/earth2me/essentials/EssentialsServerListener.java

@@ -12,6 +12,7 @@ import java.util.Iterator;
 
 public class EssentialsServerListener implements Listener {
     private final transient IEssentials ess;
+    private boolean errorLogged = false;
 
     public EssentialsServerListener(final IEssentials ess) {
         this.ess = ess;
@@ -19,11 +20,19 @@ public class EssentialsServerListener implements Listener {
 
     @EventHandler(priority = EventPriority.LOWEST)
     public void onServerListPing(final ServerListPingEvent event) {
-        Iterator<Player> iterator = event.iterator();
-        while (iterator.hasNext()) {
-            Player player = iterator.next();
-            if (ess.getUser(player).isVanished()) {
-                iterator.remove();
+        try {
+            Iterator<Player> iterator = event.iterator();
+            while (iterator.hasNext()) {
+                Player player = iterator.next();
+                if (ess.getUser(player).isVanished()) {
+                    iterator.remove();
+                }
+            }
+        } catch (UnsupportedOperationException e) {
+            if (!errorLogged) {
+                ess.getLogger().warning("Current server implementation does not support "
+                    + "hiding players from server list ping. Update or contact the maintainers.");
+                errorLogged = true;
             }
         }
     }