Invalid path: 'null.id'

Code:

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1080 [main] ERROR org.hibernate.hql.PARSER -  Invalid path: 'null.id'
1080 [main] ERROR org.hibernate.hql.PARSER - <AST>:0:0: unexpected end of subtree
1080 [main] ERROR org.hibernate.hql.PARSER -  left-hand operand of a binary operator was null
1080 [main] ERROR org.hibernate.hql.PARSER - <AST>:0:0: unexpected end of subtree
1138 [main] ERROR org.hibernate.impl.SessionFactoryImpl - Error in named query: findSensorGroupBySensorId
org.hibernate.hql.ast.QuerySyntaxException: Invalid path: 'null.id' [SELECT sgroup FROM com.pointsix.model.security.SensorGroup AS sgroup, com.pointsix.model.security.SensorGroupEntry AS entry, com.pointsix.model.sensor.Sensor WHERE Sensor.id = ?  AND entry.sensorId = Sensor.id  AND sgroup.id = entry.sensorGroupId ]

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Hibernate gave me this error on my query. I'm unsure as to how to proceed.

How can one of the properties be null in this circumstance?

Nevermind. Figured it out. Had the sensor ID twice essentially. It must have been confusing the compiler.