Java 17: guide with Concurrent HashMap and Stream API - Unexpected NullPointerException
I'm building a feature where I'm trying to configure I'm working on a project and hit a roadblock... I'm working with a `NullPointerException` when trying to use the Java 17 Stream API to process entries in a `ConcurrentHashMap`. I have a `ConcurrentHashMap<String, String>` that is populated by multiple threads, and I want to filter and collect the non-null values into a list. Here's what I've tried: ```java ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>(); map.put("key1", "value1"); map.put("key2", null); map.put("key3", "value3"); List<String> nonNullValues = map.entrySet().stream() .filter(entry -> entry.getValue() != null) .map(Map.Entry::getValue) .collect(Collectors.toList()); ``` When I run this code, I randomly get a `NullPointerException` at the `filter` step. I thought that using `ConcurrentHashMap` would handle concurrent modifications safely. I even surrounded the stream processing with a synchronized block, but the scenario continues. Is there a specific reason why I'm getting a `NullPointerException` here? Should I be using a different approach to make sure that I don't run into this scenario? Any insights or best practices would be greatly appreciated. I'd love to hear your thoughts on this. Has anyone else encountered this? I'm using Java stable in this project. What's the best practice here?