Add null-checks in all `LoginModule` implementations. It's possible that an application calls `logout` after a login failure, where most internal variables for principals and credentials are null and removing a null from the `Subject`'s principals and credentials sets will trigger a `NullPointerException`.
------------- Commit messages: - more null check inside collections - implSpec, some javadoc cstyle change - the fix Changes: https://git.openjdk.org/jdk/pull/9348/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9348&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8282730 Stats: 199 lines in 9 files changed: 148 ins; 2 del; 49 mod Patch: https://git.openjdk.org/jdk/pull/9348.diff Fetch: git fetch https://git.openjdk.org/jdk pull/9348/head:pull/9348 PR: https://git.openjdk.org/jdk/pull/9348
