Hive UDTF - unable to fetch field names via getFieldName, it is returning _col0,_col1 - hadoop

Question

I am working on Hive UDTF to transpose each row around primary key. as part of requirement, i need to associate column name and corresponding data with the key.
e.g.
Source Data
Customer_id Customer_name Customer_type
1000000 ABCD Individual
Hive UDTF will convert the data into following
Key att_name att_val
10000000 customer_name ABCD
10000000 customer_type Individual
i have written the udtf and it is working and currently producing below data
Key att_name att_val
10000000 _col0 ABCD
10000000 _col1 Individual
here is the code in which (StructField)inputFields.get(i)).getFieldName() is returning _col0 instead of customer_name.
could this be a probable defect in apache hive or there is yet another mapping for _col0 to actual schema that i should refer to.
public class transposeUDTF extends GenericUDTF {
private Map tableMap = new HashMap();
private MetadataListStructObjectInspector metadataDetails;
#Override
public StructObjectInspector initialize(StructObjectInspector args) throws UDFArgumentException {
List inputFields = args.getAllStructFieldRefs();
((StructObjectInspector)args).getTypeName();
for(int i = 0; i < inputFields.size(); ++i)
{
tableMap.put(i+1,((StructField)inputFields.get(i)).getFieldName());
}
return super.initialize(args);
}
#Override
public StructObjectInspector initialize(ObjectInspector[] argOIs) throws UDFArgumentException {
List<String> fieldNames = new ArrayList<String>(3);
List<ObjectInspector> fieldOIs = new ArrayList<ObjectInspector>(3);
fieldNames.add("key");
fieldNames.add("AttrName");
fieldNames.add("AttrVal");
fieldOIs.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);
fieldOIs.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);
fieldOIs.add(PrimitiveObjectInspectorFactory.javaStringObjectInspector);
return ObjectInspectorFactory.getStandardStructObjectInspector(fieldNames, fieldOIs);
}
#Override
public void process(Object[] record) throws HiveException {
ArrayList<Object[]> results = new ArrayList<Object[]>();
for(int i = 1; i < record.length; ++i) {
results.add(new Object[] {record[0],tableMap.get(i).toString(),record[i]});
}
Iterator<Object[]> it = results.iterator();
while (it.hasNext()){
Object[] r = it.next();
forward(r);
}
}
#Override
public void close() throws HiveException {
// do nothing
}
}