Github user JoshRosen commented on the pull request:

    https://github.com/apache/spark/pull/6361#issuecomment-109171615
  
    Trying to dig into the stracktrace a bit:, here an excerpt from 
GenericUDTFExplode.java in hive-exec-0.13.1a-sources.jar:
    
    ```java
      private transient final Object[] forwardListObj = new Object[1];
      private transient final Object[] forwardMapObj = new Object[2];
    
      @Override
      public void process(Object[] o) throws HiveException {
        switch (inputOI.getCategory()) {
        case LIST:
          ListObjectInspector listOI = (ListObjectInspector)inputOI;
          List<?> list = listOI.getList(o[0]);
          if (list == null) {
            return;
          }
          for (Object r : list) {
            forwardListObj[0] = r;    // <------- line 93 that throws NPE
            forward(forwardListObj);
          }
          break;
    ```
    
    Based on the line number, I think that the NPE is being thrown because the 
transient field `forwardListObj` is null`.  Since this field is `transient 
final` I wonder if this class wasn't designed to have its `process` method 
called on deserialized instances.  If that's the case, though, I'm puzzled at 
why we wouldn't see similar behavior with Java serialization.  The problem must 
be a bit deeper and merits more investigation.


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