Address review comments. Added more test cases

Author: rdsr

mr/src/main/java/org/apache/iceberg/mr/SerializationUtil.java

@@ -28,7 +28,6 @@
 import java.util.Base64;
 import org.apache.iceberg.exceptions.RuntimeIOException;
 
-
 public class SerializationUtil {
 
   private SerializationUtil() {