Fix null messages

SpigotCore_Main/src/de/steamwar/core/ErrorHandler.java

@@ -53,6 +53,8 @@ public class ErrorHandler extends Handler {
             return;
 
         String message = logRecord.getMessage();
+        if(message == null)
+            message = "";
         for(String reason : ignoreStartsWith)
             if(message.startsWith(reason))
                 return;