Don't assume Essentials is running.

src/main/java/com/massivecraft/factions/integration/Essentials.java

@@ -38,6 +38,9 @@ public class Essentials {
     }
 
     public static boolean isVanished(Player player) {
+        if(essentials == null) {
+            return false;
+        }
         return essentials.getUser(player).isVanished();
     }
 }