JSON SerDe issues

1) JsonSerDe uses the column names specified in the data instead of the schema for serialization : The JSON SerDe uses column names as specified in the data for serialization instead of relying on the schema provided during initialize. This is good for position-independent serialization if the object were to not be so, but it breaks when the objectinspector being provided to the serializer does not use the same names. A case in point is with the RCFile Object Inspector, which uses generic "col0", "col1" names for the top level object.

2) Does not handle null complex fields. nulls for simple types are handled, but not for complex types. SerDe expects empty array( [] ) or empty map( {} ) or empty struct( {} ) instead of null.