shuai-xu opened a new pull request #11068: [FLINK-15964] [cep] fix getting event of previous stage in notFollowedBy may throw exception bug URL: https://github.com/apache/flink/pull/11068 ## What is the purpose of the change This pull request fixes the bug that when getting the events in previous stage in notFollowedBy, it may throw exceptions. For example: ``` Pattern.begin("a").notFollowedBy("b").where(new IterativeCondition<Event>() { @Override public boolean filter(Event value, Context<Event> ctx) throws Exception { return value.getName().equals(ctx.getEventsForPattern("a").iterator().next().getName()); } }).followedBy(""c); ``` will throw exception at running. ## Verifying this change This change added tests and can be verified as follows: - *Added tests in NFAITCase* ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): (no) - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (no) - The serializers: (no) - The runtime per-record code paths (performance sensitive): (no) - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no) - The S3 file system connector: (no) ## Documentation - Does this pull request introduce a new feature? (no) - If yes, how is the feature documented? (not applicable)
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