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Posted to issues@jena.apache.org by GitBox <gi...@apache.org> on 2022/07/18 10:58:24 UTC
[GitHub] [jena] namedgraph opened a new issue, #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
namedgraph opened a new issue, #1450:
URL: https://github.com/apache/jena/issues/1450
### Version
4.5.0
### What happened?
Writing Model as RDF/XML started giving this exception. I cannot pinpoint any changes that could have caused it, the code in this area has been stable for a long time. I can serialize the same model as Turtle (and then re-serialize as RDF/XML using riot CLI) just fine. The data can be provided if it helps.
Some investigation I did:
* `this.getPrefixFor( value )` returns `null`, where value is `http://www.w3.org/2001/XMLSchema#`: https://github.com/apache/jena/blob/main/jena-core/src/main/java/org/apache/jena/rdfxml/xmloutput/impl/BaseXMLWriter.java#L229
* `Relation::backwards` returns `null` because `http://www.w3.org/2001/XMLSchema#` is not in the `cols` map: https://github.com/apache/jena/blob/main/jena-core/src/main/java/org/apache/jena/rdfxml/xmloutput/impl/Relation.java#L204
### Relevant output and stacktrace
```shell
java.lang.NullPointerException: Cannot invoke "String.equals(Object)" because "prefix" is null
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.checkLegalPrefix(BaseXMLWriter.java:845)
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.setNsPrefix(BaseXMLWriter.java:324)
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.primeNamespace(BaseXMLWriter.java:232)
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.setupNamespaces(BaseXMLWriter.java:482)
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.write(BaseXMLWriter.java:466)
org.apache.jena.rdfxml.xmloutput.impl.BaseXMLWriter.write(BaseXMLWriter.java:456)
com.atomgraph.linkeddatahub.server.io.ValidatingModelProvider.write(ValidatingModelProvider.java:129)
```
### Are you interested in making a pull request?
_No response_
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[GitHub] [jena] namedgraph closed issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
namedgraph closed issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
URL: https://github.com/apache/jena/issues/1450
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[GitHub] [jena] afs commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
afs commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1193282457
Status? If there isn't anything actionable about Jena, this should be closed.
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[GitHub] [jena] namedgraph commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
namedgraph commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1188294089
@afs I'm trying to narrow this down.
It looks like it's caused by my `OntModelReadOnly` implementation. This gives the NPE:
```
new org.apache.jena.rdfxml.xmloutput.impl.Basic().write(new OntModelReadOnly(ontModel)), System.out, null);
```
while this succeeds:
```
new org.apache.jena.rdfxml.xmloutput.impl.Basic().write(ontModel), System.out, null);
```
Could it be because my subclass is denying access to the `*NsPrefix` methods?
https://github.com/AtomGraph/Processor/blob/master/src/main/java/com/atomgraph/processor/util/OntModelReadOnly.java#L1436
I'll try allowing them.
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[GitHub] [jena] namedgraph commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
namedgraph commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1188631543
The NPE went away when I removed my implementation. I'll try to make a standalone example.
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[GitHub] [jena] namedgraph commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
namedgraph commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1188626047
That didn't help... I'll try removing `OntModelReadOnly` usages altogether.
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[GitHub] [jena] afs commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
afs commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1187280257
> The data can be provided if it helps.
A minimal, reproducible example please.
Minimal code, minimal data.
Does the example work in previous versions?
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[GitHub] [jena] namedgraph commented on issue #1450: NPE: Cannot invoke "String.equals(Object)" because "prefix" is null
Posted by GitBox <gi...@apache.org>.
namedgraph commented on issue #1450:
URL: https://github.com/apache/jena/issues/1450#issuecomment-1193659213
Nothing actionable right now because I'm on vacation. Might reopen later when I have time to build a test case.
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