SFTP Server errors with a null pointer exception

Symptom

SFTP Server errors with null pointer exception.

The error is caused when a file with the same name is received by the SFTP Server in a very close proximity in time.

Consider the scenario:
1. user1 sends one file abc.txt to the server. This makes an entry in DOCUMENT_NURSERY table.
2. Before the file tranfer completes, user1 sends the same file abc.txt again. This deletes the entry in DOCUMENT_NURSERY and makes the same entry again.
3. The first file transfer completes and it deletes the entry from DOCUMENT_NURSERY table
4. When the second file completes, it attempts to delete the entry from DOCUMENT_NURSERY table, but fails since the entry has already been deleted:
[2009-08-29 23:07:19.581] ALL 000000000000 GLOBAL_SCOPE Audit: perform public key auth
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE java.lang.NullPointerException
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at java.lang.String.<init>(String.java:261)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.workflow.DocumentNurseryRecord.getKeyBlobId(Docum entNurseryRecord.java:383)

noapp.log:

c3704e955774c8af:1dc5e23:12361a5274a:-7fe1
[2009-08-29 23:07:19.581] ALL 000000000000 GLOBAL_SCOPE Audit: perform public key auth
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE java.lang.NullPointerException
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at java.lang.String.<init>(String.java:261)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.workflow.DocumentNurseryRecord.getKeyBlobId(Docum entNurseryRecord.java:383)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.workflow.DocumentNurseryRecord.complete(DocumentN urseryRecord.java:282)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.services.sftpserver.server.MessageReaderWriterBas e.closeSucceeded(MessageReaderWriterBase.java:158)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.services.sftpserver.server.MessageOperation.close (MessageOperation.java:272)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.services.sftpserver.server.MessageProvider.close( MessageProvider.java:170)
[2009-08-29 23:07:24.442] ALL 000000000000 GLOBAL_SCOPE at com.sterlingcommerce.woodstock.services.sftpserver.server.MailboxSystemProvider. closeFile(MailboxSystemProvider.java:691)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.SftpSubsystem$_K.run(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.SftpSubsystem$_T.A(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.SftpSubsystem.onMessageReceived(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.Subsystem.processMessage(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.SessionChannel.onChannelData(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.Channel.A(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.ConnectionProtocol.E(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.ConnectionProtocol.processMessage(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.TransportProtocol.A(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.TransportProtocol.B(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.sshd.TransportProtocol.onSocketRead(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.nio.SocketConnection.processReadEvent(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.nio.Daemon$_C.processSelectionKey(Unknown Source)
[2009-08-29 23:07:24.445] ALL 000000000000 GLOBAL_SCOPE at com.maverick.nio.SelectorThread.run(Unknown Source)