How to use the pouchdb-errors.MISSING_DOC function in pouchdb-errors

stores.bySeqStore.get(formatSeq(seq), function (err, doc) {
        if (!doc) {
          return callback(pouchdbErrors.createError(pouchdbErrors.MISSING_DOC));
        }
        /* istanbul ignore if */
        if ('_id' in doc && doc._id !== metadata.id) {
          // this failing implies something very wrong
          return callback(new Error('wrong doc returned'));
        }
        doc._id = metadata.id;
        if ('_rev' in doc) {
          /* istanbul ignore if */
          if (doc._rev !== rev) {
            // this failing implies something very wrong
            return callback(new Error('wrong doc returned'));
          }
        } else {
          // we didn't always store this
          doc._rev = rev;

stores.bySeqStore.get(formatSeq(seq), function (err, doc) {
        if (!doc) {
          return callback(pouchdbErrors.createError(pouchdbErrors.MISSING_DOC));
        }
        /* istanbul ignore if */
        if ('_id' in doc && doc._id !== metadata.id) {
          // this failing implies something very wrong
          return callback(new Error('wrong doc returned'));
        }
        doc._id = metadata.id;
        if ('_rev' in doc) {
          /* istanbul ignore if */
          if (doc._rev !== rev) {
            // this failing implies something very wrong
            return callback(new Error('wrong doc returned'));
          }
        } else {
          // we didn't always store this
          doc._rev = rev;