We don't use Checker, we tried it and it was too buggy/complex. We use IntelliJ itself to do the checks (so they don't run on every compilation, but they do run every time you change something) - you can configure it to treat null issues as errors instad of warnings. This is of course not 100% but it doesn't need to be, tests and code-review tend to catch the remaining places where we forgot to check for null.
NullPointerException is really rare in our codebase which is a few million lines of code (something like 80% Java, 20% Kotlin), so I wouldn't call it a major issue or even a minor issue.
At work, everyone has the choice to write code in either Java or Kotlin and most people, most of the time, stick with Java, so the percentage of Kotlin code is not increasing, it's mostly stable lately.
NullPointerException is really rare in our codebase which is a few million lines of code (something like 80% Java, 20% Kotlin), so I wouldn't call it a major issue or even a minor issue.
At work, everyone has the choice to write code in either Java or Kotlin and most people, most of the time, stick with Java, so the percentage of Kotlin code is not increasing, it's mostly stable lately.