public static UnionStructObjectInspector getUnionStructObjectInspector(
      List<StructObjectInspector> structObjectInspectors) {
    UnionStructObjectInspector result = cachedUnionStructObjectInspector.getIfPresent(structObjectInspectors);
    if (result == null) {
      result = new UnionStructObjectInspector(structObjectInspectors);
      cachedUnionStructObjectInspector.put(structObjectInspectors, result);
    }
    return result;
  }
Verify that we don't have an unexpected type of object inspector.
@param option The option to verify
@param oi The ObjectInspector to verify
@param checkOption We're only interested in this option type
@param classes ObjectInspector should not be of these types
serde/src/java/org/apache/hadoop/hive/serde2/objectinspector/ObjectInspectorFactory.java