How to get attachment from document, I stored attachment which is contains "crl_2792.crl: {content_type: "application/pkix-crl", revpos: 2, digest: "md5-CwFLMeP+A6KlQMvC4YiFlw==", length: 797, stub: true}}}

i am trying to get attachment using below code db.getAttachment(id, attachment);

i could not attachment body parameter so please help me to solve the above problem thanks in advance