address comments

Author: Davies Liu

examples/src/main/python/streaming/kafka_wordcount.py

@@ -21,7 +21,7 @@
 
  To run this on your local machine, you need to setup Kafka and create a producer first, see
  http://kafka.apache.org/documentation.html#quickstart
- 
+
  and then run the example
     `$ bin/spark-submit --driver-class-path external/kafka-assembly/target/scala-*/\
       spark-streaming-kafka-assembly-*.jar examples/src/main/python/streaming/kafka_wordcount.py \

python/pyspark/serializers.py

@@ -146,7 +146,7 @@ def _read_with_length(self, stream):
         length = read_int(stream)
         if length == SpecialLengths.END_OF_DATA_SECTION:
             raise EOFError
-        if length == SpecialLengths.NULL:
+        elif length == SpecialLengths.NULL:
             return None
         obj = stream.read(length)
         if len(obj) < length: