# Apache Lucene Migration Guide

## Separation of IndexDocument and StoredDocument (LUCENE-3312)

The API of oal.document was restructured to differentiate between stored 
documents and indexed documents. IndexReader.document(int) now returns 
StoredDocument instead of Document. In most cases a simple replacement
of the return type is enough to upgrade.

## FunctionValues.exist() Behavior Changes due to ValueSource bug fixes (LUCENE-5961)

Bugs fixed in several ValueSource functions may result in different behavior in 
situations where some documents do not have values for fields wrapped in other 
ValueSources.  Users who want to preserve the previous behavior may need to wrap 
their ValueSources in a "DefFunction" along with a ConstValueSource of "0.0".