upgrade from Lucene 1.3 final to 1.4rc3 problem

[Alex Aw Seat Kiong]

Hi!

I'm using Lucene 1.3 final currently, all things were working fine.
But, after i'm upgraded from Lucene 1.3 final to 1.4rc3 (simply overwrite the 
lucene-1.4-final.jar to lucene-1.4-rc3.jar and re-compile it)
We can re-compile it successfuly. but when will try to index the document. It give the 
error as below:
java.lang.NullPointerException
        at org.apache.lucene.store.FSDirectory.create(FSDirectory.java:146)
        at org.apache.lucene.store.FSDirectory.<init>(FSDirectory.java:126)
        at org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:102)
        at org.apache.lucene.store.FSDirectory.getDirectory(FSDirectory.java:83)
        at org.apache.lucene.index.IndexWriter.<init>(IndexWriter.java:173)
Which wrong? Pls help.

Thanks.

Regards,
Alex