Change ErrorHandler interface to abstract class

Author: komamitsu

src/main/java/org/fluentd/logger/errorhandler/ErrorHandler.java

@@ -2,6 +2,6 @@
 
 import java.io.IOException;
 
-public interface ErrorHandler {
-    void handleNetworkError(IOException ex);
+public abstract class ErrorHandler {
+    public void handleNetworkError(IOException ex) {};
 }

src/main/java/org/fluentd/logger/errorhandler/NullErrorHandler.java

@@ -18,7 +18,6 @@
 package org.fluentd.logger.sender;
 
 import org.fluentd.logger.errorhandler.ErrorHandler;
-import org.fluentd.logger.errorhandler.NullErrorHandler;
 import org.msgpack.MessagePack;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -35,7 +34,7 @@ public class RawSocketSender implements Sender {
 
     private static final Logger LOG = LoggerFactory.getLogger(RawSocketSender.class);
 
-    private static final ErrorHandler DEFAULT_ERROR_HANLDER = new NullErrorHandler();
+    private static final ErrorHandler DEFAULT_ERROR_HANLDER = new ErrorHandler() {};
 
     private MessagePack msgpack;