@Override
  protected List<TypeInfo> parseColumnTypes() {
    List<TypeInfo> columnTypes = super.parseColumnTypes();
    return (!columnTypes.isEmpty()) ? columnTypes
        : Collections.nCopies(getColumnNames().size(), TypeInfoFactory.stringTypeInfo);
  }
NOTE: if "columns.types" is missing, all columns will be of String type.
serde/src/java/org/apache/hadoop/hive/serde2/lazy/LazySimpleSerDe.java