shinji-san opened a new issue, #3268:
URL: https://github.com/apache/jena/issues/3268
### Version
5.4
### Feature
## Description
As I understand, in SPARQL 1.1, the `UNDEF` keyword in a `VALUES` clause
represents an unbound binding (i.e. `null`). However, when I'm calling any of
the following methods in `org.apache.jena.query.ParameterizedSparqlString`
with a `null` element, a `NullPointerException` is thrown:
```java
setValues(String valueName, Collection<? extends
org.apache.jena.rdf.model.RDFNode> items)
setValues(String valueName, org.apache.jena.rdf.model.RDFNode item)
setValues(Map<String, Collection<? extends
org.apache.jena.rdf.model.RDFNode>> itemsMap)
```
There is also no existing `RDFNode` implementation that represents the
SPARQL keyword `UNDEF`. According to the SPARQL 1.1 specification, `UNDEF` must
be allowed in a VALUES clause to represent an unbound binding.
## Actual Behavior
- A `NullPointerException` occurs
- No way to explicitly represent the `UNDEF` keyword via the API
## Expected Behavior
- No `NullPointerException` is thrown
- The generated query is valid SPARQL:
```sparql
VALUES (?x ?y) {
(:uri1 1)
(:uri2 UNDEF)
}
```
## Possible Solutions
1. Introduce an `UndefRDFNode`
- Create a class `UndefRDFNode` implements `RDFNode` whose `toString()`
returns "UNDEF".
- `ParameterizedSparqlString` detects instances of `UndefRDFNode` and
render them as `UNDEF`.
2. Treat `null` as `UNDEF`
- Modify all `setValues` methods to catch `null` entries and output
`UNDEF` instead of throwing an exception.
- Pros: No new class required.
- Cons: Overloading `null` may be confusing in other contexts.
3. Reuse an existing Node type
- Investigate if `Node.ANY` or another core Node can be repurposed to
mean unbound.
- Please note: `Node.ANY` is intended for pattern matching, not unbound
results, so semantics differ.
## Tests
Add unit tests for each overload of `setValues` method to verify that the
correct results are returned:
- Single-variable `UNDEF` case
- Mixed bindings, e.g. `( :uri1 1 )`, `( :uri2 UNDEF )`
- Multi-variable rows containing `UNDEF`
## References
- Apache JIRA: [JENA-1750](https://issues.apache.org/jira/browse/JENA-1750)
- SPARQL 1.1 Query Language: [VALUES
clause](https://www.w3.org/TR/sparql11-query/#inline-data)
### Are you interested in contributing a solution yourself?
None
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