QuerySpecValidator fails to catch errors when filterExpression has more than one objects

[DimitrisGk-iel]

Bug Report

Describe the Bug

When we issue a EDC_QUERY_SPEC_TYPE query that has a filterExpresssion with more than one objects, QuerySpecValidator fails to catch it.

Expected Behavior

A message that the operandLeft is missing e.g.
{"message":"mandatory value 'https://w3id.org/edc/v0.0.1/ns/filterExpression/https://w3id.org/edc/v0.0.1/ns/operandLeft' is missing or it is blank","type":"ValidationFailure","path":"[https://w3id.org/edc/v0.0.1/ns/filterExpression/https://w3id.org/edc/v0.0.1/ns/operandLeft","invalidValue":null}]

Observed Behavior

SEVERE 2023-09-06T00:01:58.1307352 JerseyExtension: Unexpected exception caught
java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at org.eclipse.edc.spi.query.Criterion$Builder.build(Criterion.java:132)
	at org.eclipse.edc.core.transform.transformer.to.JsonObjectToCriterionTransformer.transform(JsonObjectToCriterionTransformer.java:51)
	at org.eclipse.edc.core.transform.transformer.to.JsonObjectToCriterionTransformer.transform(JsonObjectToCriterionTransformer.java:29)
	at org.eclipse.edc.core.transform.Transfo

Steps to Reproduce

Steps to reproduce the behavior:

1. Issue the above query to the /v3/assets/request endpoint
2. See error

Context Information

• Used version EDC v0.2.1

Detailed Description

If applicable, add screenshots and logs to help explain your problem.

Possible Implementation

CriterionValidator should be run on all filterExpression objects and not just the first one

[github-actions]

Thanks for your contribution 🔥 We will take a look asap 🚀

[github-actions]

This issue is stale because it has been open for 14 days with no activity.

[ndr-brt]

At a glance, the issue should be caused by the wrong definition for the filterExpression validator, it should be verifyArrayItem instead of verifyObject.

Connector/core/common/validator-core/src/main/java/org/eclipse/edc/validator/jsonobject/validators/model/QuerySpecValidator.java

Line 49 in f981237

.verifyObject(EDC_QUERY_SPEC_FILTER_EXPRESSION, CriterionValidator::instance);

[arnoweiss]

logically, multiple filterExpressions are AND-chained, right?

[ndr-brt]

@arnoweiss yes, they are