kafka-1797; (addressing Manikumar Reddy's comment) add the serializer/deserializer api to the new java client; patched by Jun Rao; reviewed by Manikumar Reddy and Neha Narkhede

clients/src/main/java/org/apache/kafka/common/serialization/StringDeserializer.java

@@ -37,7 +37,10 @@ public class StringDeserializer implements Deserializer<String> {
     @Override
     public String deserialize(String topic, byte[] data) {
         try {
-            return new String(data, encoding);
+            if (data == null)
+                return null;
+            else
+                return new String(data, encoding);
         } catch (UnsupportedEncodingException e) {
             throw new SerializationException("Error when deserializing byte[] to string due to unsupported encoding " + encoding);
         }

clients/src/main/java/org/apache/kafka/common/serialization/StringSerializer.java

@@ -37,7 +37,10 @@ public class StringSerializer implements Serializer<String> {
     @Override
     public byte[] serialize(String topic, String data) {
         try {
-            return data.getBytes(encoding);
+            if (data == null)
+                return null;
+            else
+                return data.getBytes(encoding);
         } catch (UnsupportedEncodingException e) {
             throw new SerializationException("Error when serializing string to byte[] due to unsupported encoding " + encoding);
         }

clients/src/test/java/org/apache/kafka/common/serialization/SerializationTest.java

@@ -48,8 +48,10 @@ public class SerializationTest {
 
             assertEquals("Should get the original string after serialization and deserialization with encoding " + encoding,
                     str, deserializer.deserialize(mytopic, serializer.serialize(mytopic, str)));
-        }
 
+            assertEquals("Should support null in serialization and deserialization with encoding " + encoding,
+                    null, deserializer.deserialize(mytopic, serializer.serialize(mytopic, null)));
+        }
     }
 
     private SerDeser<String> getStringSerDeser(String encoder) {