How do create an Alert filter for an empty resource

Summary:

I want to create an Alert for learnerLearningRecords, that trigger when learnerLearningRecords/learningItemRelatedMaterials

is empty. How do can I do that? I've tried creating a filter for learnerLearningRecords/learningItemRelatedMaterials and adding the expression ${attachmentName} IS NULL.

Content (required):

I want to create an Alert for learnerLearningRecords, that trigger when learnerLearningRecords/learningItemRelatedMaterials

is empty. How do can I do that? I've tried creating a filter for learnerLearningRecords/learningItemRelatedMaterials and adding the expression ${attachmentName} IS NOT NULL.

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