Passing empty collections to derived finder methods lead to a `NullPointerException`.

[pelletier197]

It seems to raise an exception when a provided parameter is an empty iterable (I have only tried with Set actually, but looking at the code that raises the error, it's likely the same thing with all Iterable<?>).

Given the following example (the database does not actually matter)

interface TestPersonRepository : Neo4jRepository<PersonEntity, String> {
    @Query(
        """
        MATCH (person:Person) WHERE person.email IN $${"emails"} OR person.name IN $${"names"}
        RETURN person
    """
    )
    fun findAllByNamesOrEmail(names: Set<String>, emails: Set<String>) : List<PersonEntity>
}

@Service
class TestService(
    private val repository: TestPersonRepository
) {
    init {
            repository.findAllByNamesOrEmail(emptySet(), setOf("potato"))
    }
}

I have the following stacktrace

Caused by: java.lang.IllegalArgumentException: Type must not be null!
	at org.springframework.util.Assert.notNull(Assert.java:201)
	at org.springframework.data.mapping.context.AbstractMappingContext.hasPersistentEntityFor(AbstractMappingContext.java:211)
	at org.springframework.data.neo4j.repository.query.Neo4jQuerySupport.convertParameter(Neo4jQuerySupport.java:190)
	at org.springframework.data.neo4j.repository.query.Neo4jQuerySupport.convertParameter(Neo4jQuerySupport.java:160)
	at org.springframework.data.neo4j.repository.query.StringBasedNeo4jQuery.lambda$bindParameters$8(StringBasedNeo4jQuery.java:218)
	at java.base/java.lang.Iterable.forEach(Iterable.java:75)
	at org.springframework.data.neo4j.repository.query.StringBasedNeo4jQuery.bindParameters(StringBasedNeo4jQuery.java:213)
	at org.springframework.data.neo4j.repository.query.StringBasedNeo4jQuery.prepareQuery(StringBasedNeo4jQuery.java:180)
	at org.springframework.data.neo4j.repository.query.AbstractNeo4jQuery.execute(AbstractNeo4jQuery.java:84)
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137)
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121)
	// ...

The error actually seem to be in org.springframework.data.neo4j.core.TemplateSupport.findCommonElementType which returns a null class when the collection is empty.

I'm testing using the latest 6.1.2. Hope this helps!

[michael-simons]

Thanks @pelletier197 that helps a lot. It's an oversight from #2292. Luckily you caught this just before the impending release.