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https://issues.apache.org/jira/browse/FLINK-18961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17178007#comment-17178007
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Kenneth William Krugler commented on FLINK-18961:
-------------------------------------------------
Hi [~chesnay] - the exception is clear, but I see this biting a lot of new
Flink users. I think it would be worthwhile to add a warning to the
[MapFunction|http://[https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/api/common/functions/MapFunction.html]]
documentation, that says something about never returning a null value, and
using a FlatmapFunction as an alternative is results could be negative.
> In the case of FlatMap linking map, if map returns null, an exception will
> be thrown in FlatMap
> ------------------------------------------------------------------------------------------------
>
> Key: FLINK-18961
> URL: https://issues.apache.org/jira/browse/FLINK-18961
> Project: Flink
> Issue Type: Bug
> Components: API / DataSet
> Affects Versions: 1.11.0
> Environment: Mac OS 10.13.6
> Kubernetes 1.16.8
> Flink 1.11.0
> Reporter: Ryan
> Priority: Minor
> Attachments: Lark20200814-173817.png, Lark20200814-173821.png,
> Lark20200814-173824.png
>
>
> I found a DateSet problem. In the case of FlatMap linking map, if map
> returns null, an exception will be thrown in FlatMap.I think it's a problem
> with the operator chain.I will post a screenshot of the corresponding stack
> call in the attachment.
> {code:java}
> text.filter(value -> value.f0.contains("any")).flatMap(new
> FlatMapFunction<Tuple2<String, String>, String>() {
> @Override
> public void flatMap(Tuple2<String, String> value,
> Collector<String> out) throws Exception {
> Pattern pattern = Pattern.compile("\".*\"");
> Matcher matcher = pattern.matcher(value.f0);
> if(matcher.find()){
> String match = matcher.group(0);
> out.collect(match); // here throw Exception
> }
> }
> }).map(value -> {
> try {
> String jsonS = value.replace("\"\"","\"");
> jsonS = jsonS.substring(1,jsonS.length()-1);
> JSONObject json = JSONObject.parseObject(jsonS);
> String result =
> json.getJSONObject("body").getJSONObject("message").getString("data");
> return result; // this is null
> }catch (Exception e){
> return value;
> }
> }).print();
> Caused by: java.lang.NullPointerException: The system does not support
> records that are null. Null values are only supported as fields inside other
> objects.Caused by: java.lang.NullPointerException: The system does not
> support records that are null. Null values are only supported as fields
> inside other objects. at
> org.apache.flink.runtime.operators.shipping.OutputCollector.collect(OutputCollector.java:76)
> at
> org.apache.flink.runtime.operators.util.metrics.CountingCollector.collect(CountingCollector.java:35)
> at
> org.apache.flink.runtime.operators.chaining.ChainedMapDriver.collect(ChainedMapDriver.java:79)
> at
> org.apache.flink.runtime.operators.util.metrics.CountingCollector.collect(CountingCollector.java:35)
> at com.lemonbox.Test$1.flatMap(Test.java:42) at
> com.lemonbox.Test$1.flatMap(Test.java:35) at
> org.apache.flink.runtime.operators.chaining.ChainedFlatMapDriver.collect(ChainedFlatMapDriver.java:80)
> at
> org.apache.flink.runtime.operators.util.metrics.CountingCollector.collect(CountingCollector.java:35)
> at
> org.apache.flink.api.java.operators.translation.PlanFilterOperator$FlatMapFilter.flatMap(PlanFilterOperator.java:58)
> at
> org.apache.flink.runtime.operators.chaining.ChainedFlatMapDriver.collect(ChainedFlatMapDriver.java:80)
> at
> org.apache.flink.runtime.operators.util.metrics.CountingCollector.collect(CountingCollector.java:35)
> at
> org.apache.flink.runtime.operators.DataSourceTask.invoke(DataSourceTask.java:196)
> at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:721) at
> org.apache.flink.runtime.taskmanager.Task.run(Task.java:546) at
> java.lang.Thread.run(Thread.java:748)
> {code}
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