Java.Lang.Nullpointerexception Element Cannot Be Mapped To A Null Key | Null Pointer Exception Java Fix 상위 71개 답변

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java.lang.nullpointerexception element cannot be mapped to a null key 주제에 대한 자세한 내용은 여기를 참조하세요.

NullPointerException: element cannot be mapped to a null key

Use Collectors.toMap instead and specify that a HashMap is used (as it allows one null key) Collectors.toMap( MappingEntry::getMilestone …

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Source: stackoverflow.com

Date Published: 10/11/2022

View: 8353

element cannot be mapped to a null key” : PY-29170

Inspections stuck in error state in editor; “java.lang.NullPointerException: element cannot be mapped to a null key”. My inspections appear to get stuck in …

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Source: youtrack.jetbrains.com

Date Published: 4/6/2021

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“Element cannot be mapped to a null key” is sometimes … – PTC

NullPointerException: element cannot be mapped to a null key at java.base/java.util.Objects.requireNonNull(Objects.java:246) at java.base/java.

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Source: www.ptc.com

Date Published: 2/9/2021

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NullPointerException: element cannot be mapped to a null key

Caused by: java.lang.NullPointerException: element cannot be mapped to a null key at java.util.Objects.requireNonNull(Objects.java:228) at java.util.stream.

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Source: askcodes.net

Date Published: 1/14/2022

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NullPointerException: element cannot be mapped to a null key

报错java.lang.NullPointerException:elementcannotbemappedtoanullkey问题代码importjava.util.ArrayList;importjava.util.stream.Collectors;importlombok.

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Source: itcn.blog

Date Published: 10/21/2021

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element cannot be mapped to a null key – CUBA.Platform

When trying to show ‘my tasks’. java.lang.NullPointerException: element cannot be mapped to a null key at java.util.Objects.

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Source: forum.cuba-platform.com

Date Published: 4/22/2022

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NullPointerException: element cannot be mapped to a null key

Use Collectors.toMap instead and specify anycodings_java that a HashMap is used (as it allows one anycodings_java null key) Collectors.

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Source: www.anycodings.com

Date Published: 9/5/2022

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java.lang.NullPointerException: element cannot be mapped to …

java.lang.NullPointerException: element cannot be mapped to a null key … Collectors.lambda$groupingBy$53(Collectors.java:1127).

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Date Published: 11/18/2022

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Null Pointer Exception Java Fix
Null Pointer Exception Java Fix

주제에 대한 기사 평가 java.lang.nullpointerexception element cannot be mapped to a null key

  • Author: Alex Lee
  • Views: 조회수 99,491회
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  • Date Published: 최초 공개: 2019. 3. 8.
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NullPointerException: element cannot be mapped to a null key

I have read the topic:

Collectors.groupingBy doesn’t accept null keys

But I don’t understand how can I apply it for my issue:

my code:

Map> mappingEntryMap = mapping.getMappingEntries() .stream() .collect(Collectors.groupingBy(MappingEntry::getMilestone, Collectors.mapping(e -> e, Collectors.toList())));

For me MappingEntry::getMilestone sometimes can return null. It is ok for my situation but I see:

Caused by: java.lang.NullPointerException: element cannot be mapped to a null key at java.util.Objects.requireNonNull(Objects.java:228) at java.util.stream.Collectors.lambda$groupingBy$45(Collectors.java:907) at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)

How can I avoid this exception?

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"Element cannot be mapped to a null key" is sometimes produced when selecting an object in BOM Transformer while "Made From" tab is active in WIndchill MPMLink 12.0.2

ERROR [DataSource Task Executor-246] com.ptc.cat.ops.server.internal.NavigateOperation – java.lang.NullPointerException: element cannot be mapped to a null key wt.util.WTException: java.lang.NullPointerException: element cannot be mapped to a null key Nested exception is: java.lang.NullPointerException: element cannot be mapped to a null key at java.base/java.util.Objects.requireNonNull(Objects.java:246) at java.base/java.util.stream.Collectors.lambda$groupingBy$53(Collectors.java:1127) at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169) at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1603) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) |…]

NullPointerException: element cannot be mapped to a null key

Problem :

I have read the topic:

Collectors.groupingBy doesn’t accept null keys

But I don’t understand how can I apply it for my issue:

my code:

Map> mappingEntryMap = mapping.getMappingEntries() .stream() .collect(Collectors.groupingBy(MappingEntry::getMilestone, Collectors.mapping(e -> e, Collectors.toList())));

For me MappingEntry::getMilestone sometimes can return null. It is ok for my situation but I see:

Caused by: java.lang.NullPointerException: element cannot be mapped to a null key at java.util.Objects.requireNonNull(Objects.java: 228 ) at java.util.stream.Collectors.lambda$groupingBy$ 45 (Collectors.java: 907 ) at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java: 169 ) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java: 1374 ) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java: 481 ) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java: 471 ) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java: 708 ) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java: 234 ) at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java: 499 )

How can I avoid this exception?

Tags : java,java-8,grouping,java-stream

Answer 1:

Use Collectors.toMap instead and specify that a HashMap is used (as it allows one null key)

Collectors.toMap( MappingEntry::getMilestone, x -> { List list = new ArrayList <>(); list.add(x); return list; }, (left, right) -> { left.addAll(right); return left; }, HashMap:: new )

Answer 2:

Given that you want to retain the MappingEntry objects regardless of when getMilestone() is null or non-null and knowing that a NullPointerException will be thrown when a particular contract in not met then we can avoid that by using a replacement key to group the MappingEntry objects which have a null milestone and yet group the other MappingEntry objects as they’re supposed to be.

Map> mappingEntryMap = mapping.getMappingEntries() .stream() .collect(groupingBy(m -> m.getMilestone() == null ? “absentMilestone” : m.getMilestone()));

The trick here is to use a ternary operator which provides a key to group all the MappingEntry objects that have a absent milestone into a single group and if the milestone is not absent then we can group by its value as you’d expect.

Answer 3:

You can use the Collector.of method for this to specify a custom collector and use a HashMap for the resulting map because according to the Java-8 docs of HashMap

[…] permits null values and the null key. […]

Collector.of( HashMap:: new , (map, e) -> map.computeIfAbsent(e.getMileStone(), k -> new ArrayList <>()).add(e), (left, right) -> { right.forEach((key,list) -> left.computeIfAbsent(key, k -> new ArrayList <>()).addAll(list)); return left; }) )

Answer 4:

In my opinion the best solution:

Use Optional.empty() instead of pasing null value.

Map, List> mappingEntryMap = mapping.getMappingEntries() .stream() .collect(Collectors.groupingBy(Optional::ofNullable, Collectors.mapping(e -> e, Collectors.toList())));

Answer 5:

use filter and get only not null data.

like

NullPointerException: element cannot be mapped to a null key-IT Blog

报错

java.lang.NullPointerException: element cannot be mapped to a null key

问题代码

import java . util . ArrayList ; import java . util . stream . Collectors ; import lombok . Builder ; import lombok . Data ; @Data @Builder public class S { private String a ; private String b ; public static void main ( String [ ] args ) { ArrayList < S > list = new ArrayList < > ( ) ; list . add ( S . builder ( ) . a ( null ) . b ( “1” ) . build ( ) ) ; list . add ( S . builder ( ) . a ( null ) . b ( “2” ) . build ( ) ) ; list . add ( S . builder ( ) . a ( “a” ) . b ( “1” ) . build ( ) ) ; Map < String , List < S > > result = list . stream ( ) . collect ( Collectors . groupingBy ( S :: getA ) ) ; } }

原因

S类中的属性a的值为null，在groupingBy的元素为空时，会报上述错误

解决思路

利用 Optional.ofNullable()

具体代码

Bproc: java.lang.NullPointerException: element cannot be mapped to a null key

The Flowable engine allows empty task names. Theoretically the process definition can be deployed from the XML file created somewhere else, so I don’t think we should forbid empty task names.

Is there a way to automatically spot those NPE (with Nullable annotations or the like?)

Could you please explain what do you mean?

NullPointerException: element cannot be mapped …anycodings

I have read the topic:

Collectors.groupingBy doesn’t accept null anycodings_java-8 keys

But I don’t understand how can I apply it anycodings_java-8 for my issue:

my code:

Map> mappingEntryMap = mapping.getMappingEntries() .stream() .collect(Collectors.groupingBy(MappingEntry::getMilestone, Collectors.mapping(e -> e, Collectors.toList())));

For me MappingEntry::getMilestone sometimes anycodings_java-8 can return null. It is ok for my situation anycodings_java-8 but I see:

Caused by: java.lang.NullPointerException: element cannot be mapped to a null key at java.util.Objects.requireNonNull(Objects.java:228) at java.util.stream.Collectors.lambda$groupingBy$45(Collectors.java:907) at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)

How can I avoid this exception?

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