Shotaro Sano

@29Takuya is working on this issue

@29Takuya is no longer working on this issue due to lack of time. So, this issue is still open. Contributions are welcomed!

Adding `needs-discussion` label since the expected behavior (`None`, last intermediate value, or undefined) has not been fully agreed even among maintainers. See also this comment: https://github.com/optuna/optuna/blob/f00abac7d53bb29e53e7c8bd13e9b4be9e0f9d44/optuna/study/_tell.py#L162-L165

Since this issue has been open for a long time, let me close once. Feel free to reopen upon necessity.

Since this issue has been open for a long time, let me close once. Feel free to reopen upon necessity.

Since this issue has been open for a long time, let me close once. Feel free to reopen upon necessity.

Since this issue has been open for a long time, let me close once. Feel free to reopen upon necessity.

Since #2003 has been closed, this issue is still open.

Since this issue has been open for a long time, let me close once. Feel free to reopen upon necessity.

Sorry that I didn't explain enough. The action above is just to filter out many other out-dated issues. If the problem is still reproduced, we should reopen.