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Subject: [jira] [Commented] (FLINK-2495) Add a null point check in API
 DataStream.union
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    [ https://issues.apache.org/jira/browse/FLINK-2495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14679126#comment-14679126 ] 

ASF GitHub Bot commented on FLINK-2495:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/999#discussion_r36587360
  
    --- Diff: flink-staging/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java ---
    @@ -256,9 +256,11 @@ public ExecutionConfig getExecutionConfig() {
     		DataStream<OUT> returnStream = this.copy();
     
     		for (DataStream<OUT> stream : streams) {
    -			for (DataStream<OUT> ds : stream.unionedStreams) {
    -				validateUnion(ds.getId());
    -				returnStream.unionedStreams.add(ds.copy());
    +			if (stream != null) {
    --- End diff --
    
    Right there will be an error, but the error is helpful because it indicates a problem with the user program. 
    If the union is silently ignored, the program might behave differently from what the user expects and produce invalid results. 
    I would argue, that a `union(null)` is never intended and should be be brought to the user's attention. Also, this error might reveal more problems of the user program.


> Add a null point check in API DataStream.union
> ----------------------------------------------
>
>                 Key: FLINK-2495
>                 URL: https://issues.apache.org/jira/browse/FLINK-2495
>             Project: Flink
>          Issue Type: Bug
>          Components: Streaming
>    Affects Versions: 0.10
>            Reporter: Huang Wei
>             Fix For: 0.10
>
>   Original Estimate: 168h
>  Remaining Estimate: 168h
>
> The API(public DataStream<OUT> union(DataStream<OUT>... streams)) is a  external interface for user.
> The parameter "streams" maybe null and it will throw NullPointerException error.
> This test below can be intuitive to explain this problem:
> package org.apache.flink.streaming.api;
> import org.apache.flink.api.common.functions.MapFunction;
> import org.apache.flink.streaming.api.datastream.DataStream;
> import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
> import org.apache.flink.streaming.api.functions.source.RichParallelSourceFunction;
> import org.junit.Test;
> /**
>  * Created by HuangWHWHW on 2015/8/7.
>  */
> public class test {
> 	public static class sourceFunction extends RichParallelSourceFunction<String> {
> 		public sourceFunction() {
> 		}
> 		@Override
> 		public void run(SourceContext<String> sourceContext) throws Exception {
> 			sourceContext.collect("a");
> 		}
> 		@Override
> 		public void cancel() {
> 		}
> 	}
> 	@Test
> 	public void testUnion(){
> 		StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
> 		env.setParallelism(1);
> 		DataStream<String> source = env.addSource(new sourceFunction());
> 		DataStream<String> temp1 = null;
> 		DataStream<String> temp2 = source.map(new MapFunction<String, String>() {
> 			@Override
> 			public String map(String value) throws Exception {
> 				if (value == "a") {
> 					return "This is for test temp2.";
> 				}
> 				return null;
> 			}
> 		});
> 		DataStream<String> sink = temp2.union(temp1);
> 		sink.print();
> 		try {
> 			env.execute();
> 		}catch (Exception e){
> 			e.printStackTrace();
> 		}
> 	}
> }



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