Error message [ Exception in thread "Thread-12985214" java.lang.NullPointerException: null upcall object in mipns::Stream::Read ]

When we stress testing the MIP SDK instance (MIP SDK File Sample Source) created as a singleton in the Java Spring environment, the error occurs.

We used MIP SDK is "**mip_sdk_java_ubuntu1804_1.12.61_preview.tar.gz**", and when an error occurs during the stress testing, the **STDOUT** contents are as follows. ( https://www.microsoft.com/en-us/download/details.aspx?id=104267 )

> Exception in thread "Thread-9336141" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12966921" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12970196" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12971973" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12975081" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12985049" java.lang.NullPointerException: null upcall object in mipns::FileHandler::Observer::OnCommitSuccess
Exception in thread "Thread-12985207" java.lang.NullPointerException: null upcall object in mipns::Stream::Seek
Exception in thread "Thread-12985214" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
Exception in thread "Thread-12985218" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
Exception in thread "Thread-12985220" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
Exception in thread "Thread-12985221" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
Exception in thread "Thread-12985222" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
Exception in thread "Thread-12985224" java.lang.NullPointerException: null upcall object in mipns::Stream::Read
...
( Infinite loop output )
...
Exception in thread "Thread-12999999" java.lang.NullPointerException: null upcall object in mipns::Stream::Read

### Doing a "MIP File::Delete Label" stress test with that MIP SDK for about 5 minutes may copy the error.

`This error slows down the process and eventually crashes the process due to stack overflow.`

We have already registered with **Microsoft Case ( Case No: 32221263 )** and hope that the issue will be resolved as soon as possible.

Thanks!