Hadoop Serializer Not Found Exception

The problem was that I was making a stupid mistake: I was not updating a jar. So, basically SplitInfo was not implementing the Writable interface in the old (in use) jar.

As a general observation: the error specified in the OP has as underlying cause the fact that HADOOP can't find a Serializer for a specific type which you're trying to serialize (being directly or indirectly, e.g. by using that type as an output key/value). Hadoop cannot find a Serilizer for one of the 2 reasons:

1. your type is not serializable (i.e. it doesn't implement Writable or Serializable)
2. There is no Serializer available to Hadoop for the type of serialization your type implements (e.g.: your type implements Writable but hadoop for one reason or another cannot use the org.apache.hadoop.io.serializer.WritableSerialization class)

I think you're trying to do something you don't need to. Your output value only needs to implement the Writable interface and you should just set the output format.

conf.setOutputFormatClass(SequenceFileOutputFormat.class);

You only use the "io.serializations" configuration if you want to use a different serialization framework, which it doesn't look like you need.