NullPointerException MappingMongoConverter

[marcovmx]

Hi,

I am working with spring mongodb (1.0.0.RELEASE) and spring webflow, I am getting a null pointer exception:

java.lang.NullPointerException: null
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeMapInternal(MappingMongoConverter.java:535) ~[spring-data-mongodb-1.0.0.RELEASE.jar:na]
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:319) ~[spring-data-mongodb-1.0.0.RELEASE.jar:na]
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeMapInternal(MappingMongoConverter.java:547) ~[spring-data-mongodb-1.0.0.RELEASE.jar:na]
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writePropertyInternal(MappingMongoConverter.java:407) ~[spring-data-mongodb-1.0.0.RELEASE.jar:na]

Looking at that line in MappingMongoConverter.writeMapInternal the exception occurs in:

 if (conversions.isSimpleType(key.getClass())) {

Spring is trying to convert a null Map {null=[]}. That object is contained into a spring webflow messagesMemento object, which means I don't have control over it.

It seems this is a bug. I will be reporting it shortly.

Grettings,
Marco

[Oliver Gierke]

Besides the fact that an NPE is quite ugly here, are you saying you (or Webflow) pipe in a Map containing an entry with a null key? How shall we actually persist that one to Mongo. Just thinking about it briefly we actually either have to skip this attribute - which is not what I'd call principle of least surprise - or throw an exception rendering the entire object graph unmappable. What do you think?

[marcovmx]

Hi Oliver,

are you saying you (or Webflow) pipe in a Map containing an entry with a null key?

Yes, Webflow does it. I think throwing a more meaningful exception would help to quickly identify the problem without having to look the source code, though the occurrence of this scenario might be very low . I currently worked around it by skipping the object containing the map through my custom ConversationManager (a Webflow object), it is still under test and hope it does not have a side effect. Moreover, a better solution would come from the Webflow guys by inquiring the reason of that null key entry in the map.

Thanks,
Marco

[marcovmx]

Hi,

I am facing a different issue now,

My object to persist has an association of type org.springframework.webflow.execution.repository.i mpl.SimpleFlowExecutionSnapshotGroup, that has a property "private Map snapshots = new HashMap();".

The code flow goes all the way through CachingMongoPersistentProperty(AbstractPersistentP roperty<P>).isEntity() to evaluate if the snapshots property is of a simple type. It turns out information.getActualType() returns null, causing getType() to break. See attached image for more details.

npe-SpringMongo1.jpg
npe-SpringMongo2.jpg
npe-SpringMongo3.jpg

In my ivy.xml I have:
<dependency org="org.springframework.data" name="spring-data-mongodb" rev="1.0.0.RELEASE" />
<dependency org="org.springframework.data" name="spring-data-commons-core" rev="1.2.0.RELEASE" />

[marcovmx]

My temporary solution is changing:

	protected boolean isEntity() {
		boolean isComplexType = true;
		isComplexType = !simpleTypeHolder.isSimpleType(information.getActualType().getType());
		return isComplexType && !isTransient() && !isCollectionLike() && !isMap();
	}

for:

	protected boolean isEntity() {
		boolean isComplexType = true;
		if (!isMap()) {
			isComplexType = !simpleTypeHolder.isSimpleType(information.getActualType().getType());
		}
		return isComplexType && !isTransient() && !isCollectionLike();
	}

Not optimal but it's a pain reliever. 'information.getActualType()' returning null for a HashMap sound like a bug to me. What do you think?

[Oliver Gierke]

I'd rather say it's a bug in isEntity(). The reason we return null from a variety of methods in the TypeInformation hierarchy is that we'd like to be able to discover whether a type actually carries generic parameters or not in a variety of places. If we simply returned Object for that call there was no way to differentiate a Map from a Map<Object, Object>. Feel free to raise a Jira against Spring Data Commons.

[marcovmx]

I see...

Jira created: https://jira.springsource.org/browse/DATACMNS-132

Thanks!