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https://issues.apache.org/jira/browse/FLINK-6276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15960426#comment-15960426
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Chesnay Schepler commented on FLINK-6276:
-----------------------------------------
As far as i know the TypeHint must not contain any generic parameters but only
the actual types. When you create a TypeHint with say, Tuple2<Integer, String>,
then the information about the generic type is still available to the
TypeExtractor; it's not completely thrown away. (If i recall correctly it is
because you actually create a completely new implementation of the TypeHint)
If it would work for generics we probably wouldn't need it in the first place.
You are correct though that the error messages could be better.
> InvalidTypesException: Unknown Error. Type is null.
> ---------------------------------------------------
>
> Key: FLINK-6276
> URL: https://issues.apache.org/jira/browse/FLINK-6276
> Project: Flink
> Issue Type: Bug
> Components: Core, DataSet API
> Affects Versions: 1.2.0
> Reporter: Luke Hutchison
>
> Quite frequently when writing Flink code, I get the exception
> {{InvalidTypesException: Unknown Error. Type is null.}}
> A small example that triggers it is:
> {code}
> import java.util.ArrayList;
> import java.util.Arrays;
> import java.util.Iterator;
> import java.util.List;
> import org.apache.flink.api.java.DataSet;
> import org.apache.flink.api.java.ExecutionEnvironment;
> import org.apache.flink.api.java.tuple.Tuple2;
> import org.apache.flink.util.Collector;
> public class TestMain {
> @SafeVarargs
> public static <K, V> DataSet<Tuple2<K, List<V>>> join(V
> missingValuePlaceholder,
> DataSet<Tuple2<K, V>>... datasets) {
> DataSet<Tuple2<K, List<V>>> join = null;
> for (int i = 0; i < datasets.length; i++) {
> final int datasetIdx = i;
> if (datasetIdx == 0) {
> join = datasets[datasetIdx]
> .map(t -> {
> List<V> initialList = new ArrayList<>();
> initialList.add(t.f1);
> return new Tuple2<>(t.f0, initialList);
> })
> .name("start join");
> } else {
> join = join.coGroup(datasets[datasetIdx]) //
> .where(0).equalTo(0) //
> .with((Iterable<Tuple2<K, List<V>>> li,
> Iterable<Tuple2<K, V>> ri,
> Collector<Tuple2<K, List<V>>> out) -> {
> K key = null;
> List<V> vals = new ArrayList<>(datasetIdx + 1);
> Iterator<Tuple2<K, List<V>>> lIter =
> li.iterator();
> if (!lIter.hasNext()) {
> for (int j = 0; j < datasetIdx; j++) {
> vals.add(missingValuePlaceholder);
> }
> } else {
> Tuple2<K, List<V>> lt = lIter.next();
> key = lt.f0;
> vals.addAll(lt.f1);
> if (lIter.hasNext()) {
> throw new RuntimeException("Got
> non-unique key: " + key);
> }
> }
> Iterator<Tuple2<K, V>> rIter = ri.iterator();
> if (!rIter.hasNext()) {
> vals.add(missingValuePlaceholder);
> } else {
> Tuple2<K, V> rt = rIter.next();
> key = rt.f0;
> vals.add(rt.f1);
> if (rIter.hasNext()) {
> throw new RuntimeException("Got
> non-unique key: " + key);
> }
> }
> out.collect(new Tuple2<K, List<V>>(key, vals));
> }) //
> .name("join #" + datasetIdx);
> }
> }
> return join;
> }
> public static void main(String[] args) throws Exception {
> ExecutionEnvironment env =
> ExecutionEnvironment.getExecutionEnvironment();
> DataSet<Tuple2<String, Integer>> x = //
> env.fromElements(new Tuple2<>("a", 3), new Tuple2<>("b", 4),
> new Tuple2<>("c", 5));
> DataSet<Tuple2<String, Integer>> y = //
> env.fromElements(new Tuple2<>("b", 0), new Tuple2<>("c", 1),
> new Tuple2<>("d", 2));
> DataSet<Tuple2<String, Integer>> z = //
> env.fromElements(new Tuple2<>("c", 7), new Tuple2<>("d", 8),
> new Tuple2<>("e", 9));
> System.out.println(join(-1, x, y, z).collect());
> }
> }
> {code}
> The stacktrace that is triggered is:
> {noformat}
> Exception in thread "main"
> org.apache.flink.api.common.functions.InvalidTypesException: The return type
> of function 'join(TestMain.java:23)' could not be determined automatically,
> due to type erasure. You can give type information hints by using the
> returns(...) method on the result of the transformation call, or by letting
> your function implement the 'ResultTypeQueryable' interface.
> at org.apache.flink.api.java.DataSet.getType(DataSet.java:174)
> at
> org.apache.flink.api.java.operators.CoGroupOperator$CoGroupOperatorSets.where(CoGroupOperator.java:424)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.join(TestMain.java:27)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.main(TestMain.java:74)
> Caused by: org.apache.flink.api.common.functions.InvalidTypesException: Input
> mismatch: Unknown Error. Type is null.
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInputType(TypeExtractor.java:1134)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:409)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:349)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.getMapReturnTypes(TypeExtractor.java:164)
> at org.apache.flink.api.java.DataSet.map(DataSet.java:215)
> at
> com.rentlogic.buildingscores.flink.experimental.TestMain.join(TestMain.java:23)
> ... 1 more
> Caused by: org.apache.flink.api.common.functions.InvalidTypesException:
> Unknown Error. Type is null.
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInfo(TypeExtractor.java:1161)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInfo(TypeExtractor.java:1234)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.validateInputType(TypeExtractor.java:1131)
> ... 6 more
> {noformat}
> The code compiles fine, and typechecks. Maybe something is wrong with the
> code; but either way, Flink should report a better error message.
> A separate issue here is that the error message is being reported for the
> wrong function: the problem is not with the return type of
> {{join(TestMain.java:23)}}, it is some internal type (probably for a lambda
> or something) within the function. (It is the {{where}} clause that throws
> the exception.)
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