Processor yield NPE under some circonstancies

### Questions

When using IntelliJ > 2020.2.4 the build fails with NPE in the CodeGenProcessor.
This sound very much like an intelliJ issue however their investigation seem to aim for a lack of robustness in some processor implementations.
Here is the ticket I filled in at IntelliJ' support : https://youtrack.jetbrains.com/issue/IDEA-258659
This other ticket may be of interest too: https://youtrack.jetbrains.com/issue/IDEA-257871

### Version 3.5.3

### Context

Problem ocurred while uprading from IntelliJ 2020.2.4 to 2020.3

### Do you have a reproducer?

The following sample project builds againts intelliJ 2020.2.4 and not against 2020.3

* https://github.com/ngmip/IDEA-258659

### Steps to reproduce

1. clone repo
2. build -> rebuild project

### Extra

* windows 10 pro
* oracle jdk8u201
* For those who are looking for a workround, in the link I provided above, they explained how to configure the `-Djps.track.ap.dependencies=false` flag, this worked for me.

CodeGenProcessor とリンクされている IDEA-258659 reproducer から始めます。JDK 8 を使用して IntelliJ 2020.2.4 と 2020.3 でサンプルプロジェクトを再ビルドし、NPE がいつ発生するかを確認してから、プロセッサーの動作を IntelliJ の報告と比較します。報告されたビルド構成でプロセッサーが NPE により失敗しなくなれば完了です。

索引モデルが issue の本文から書いたものです。