Fix error in document resolver with system coresession

2018-06-18 09:19:52,488 ERROR [Nuxeo-Work-default-4] [org.nuxeo.ecm.core.work.WorkManagerImpl] Uncaught error on thread: Nuxeo-Work-default-4, current work might be lost, WorkManager metrics might be corrupted.
org.nuxeo.ecm.core.api.NuxeoException: Work failed after 0 retries, class=class org.nuxeo.labs.lambda.rekognition.worker.ImageRekognitionResultWork id=default:66dc94a9-0774-45bd-99f0-ec92caa4f036:ingest-image-rekognition category=ImageRekognitionResultWork title=default:66dc94a9-0774-45bd-99f0-ec92caa4f036:ingest-image-rekognition
        at org.nuxeo.ecm.core.work.AbstractWork.workFailed(AbstractWork.java:410)
        at org.nuxeo.ecm.core.work.AbstractWork.run(AbstractWork.java:367)
        at org.nuxeo.ecm.core.work.WorkHolder.run(WorkHolder.java:57)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
Caused by: org.nuxeo.ecm.core.api.NuxeoException: Cannot create a CoreSession outside a security context,  login() missing.
        at org.nuxeo.ecm.core.api.CoreInstance.getPrincipal(CoreInstance.java:220)
        at org.nuxeo.ecm.core.api.CoreInstance.openCoreSession(CoreInstance.java:71)
        at org.nuxeo.ecm.core.model.DocumentModelResolver.validate(DocumentModelResolver.java:148)
        at org.nuxeo.ecm.core.schema.types.constraints.ObjectResolverConstraint.validate(ObjectResolverConstraint.java:56)
        at org.nuxeo.ecm.core.api.validation.DocumentValidationServiceImpl.validateSimpleTypeField(DocumentValidationServiceImpl.java:291)
        at org.nuxeo.ecm.core.api.validation.DocumentValidationServiceImpl.validateListTypeProperty(DocumentValidationServiceImpl.java:481)
        at org.nuxeo.ecm.core.api.validation.DocumentValidationServiceImpl.validateAnyTypeProperty(DocumentValidationServiceImpl.java:381)
        at org.nuxeo.ecm.core.api.validation.DocumentValidationServiceImpl.validate(DocumentValidationServiceImpl.java:126)
        at org.nuxeo.ecm.core.api.AbstractSession.saveDocument(AbstractSession.java:1536)
        at org.nuxeo.labs.lambda.rekognition.worker.ImageRekognitionResultWork.work(ImageRekognitionResultWork.java:75)
        at org.nuxeo.ecm.core.work.AbstractWork.runWorkWithTransaction(AbstractWork.java:435)
        at org.nuxeo.ecm.core.work.AbstractWork.run(AbstractWork.java:355)
        ... 4 more