map不能返回null值吗

发现了一个问题，就是在调用map函数后，返回的null值，map的返回值为tuple2，在下一步filter过滤null值是，作业报异常。

java.lang.NullPointerException at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.copy(TupleSerializer.java:104) at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.copy(TupleSerializer.java:30) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:577) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:554) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:534) at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:689) at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:667) at org.apache.flink.streaming.api.operators.StreamMap.processElement(StreamMap.java:41) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:579) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:554) at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:534) at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:689) at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:667) at org.apache.flink.streaming.api.operators.StreamFilter.processElement(StreamFilter.java:40) at org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:202) at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:105) at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:300) at org.apache.flink.runtime.taskmanager.Task.run(Task.java:711) at java.lang.Thread.run(Thread.java:748)

经过调试发现代码中 OperatorChain 类中的 pushToOperator 方法 ，参数 record为空的情况下会报异常。 难道map 不能返回null值吗？

@Override protected void pushToOperator(StreamRecord record) { try { // we know that the given outputTag matches our OutputTag so the record // must be of the type that our operator (and Serializer) expects. @SuppressWarnings("unchecked") StreamRecord castRecord = (StreamRecord ) record;

numRecordsIn.inc(); StreamRecord copy = castRecord.copy(serializer.copy(castRecord.getValue())); operator.setKeyContextElement1(copy); operator.processElement(copy); } catch (ClassCastException e) { if (outputTag != null) { // Enrich error message ClassCastException replace = new ClassCastException( String.format( "%s. Failed to push OutputTag with id '%s' to operator. " + "This can occur when multiple OutputTags with different types " + "but identical names are being used.", e.getMessage(), outputTag.getId()));

throw new ExceptionInChainedOperatorException(replace); } else { throw new ExceptionInChainedOperatorException(e); } } catch (Exception e) { throw new ExceptionInChainedOperatorException(e); }

} } *来自志愿者整理的flink邮件归档