NullPointerException at listFiles

Hi All,

I recursively use SmbFile#listFiles method to access all folder and files.
At first, the method correctly works.
However I have the NullPointerException in about 10 minutes. 

This problem may be network environment.
But if you have any ideas to modify this problem by setting up JCIFS property,
teach me how to use the way.

<environment>
JCIFS : 1.3.16
Network access : using DFS

<stacktrace>
java.util.NullPointerException
at jcifs.smb.Dfs.resolve(Dfs.java:169)
at jcifs.smb.SmbFile.resolveDfs(SmbFile.java:671)
at jcifs.smb.SmbFile.send(SmbFile.java:773)
at jcifs.smb.SmbFile.doFindFirstNext(SmbFile.java:1986)
at jcifs.smb.SmbFile.doEnum(SmbFile.java:1738)
at jcifs.smb.SmbFile.listFiles(SmbFile.java:1715)
at jcifs.smb.SmbFile.listFiles(SmbFile.java:1704)

Thanks,
Dora