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

var att = docInfo.data._attachments[key];

        if (att.stub) {
          // still need to update the refs mapping
          var id = docInfo.data._id;
          var rev = docInfo.data._rev;
          saveAttachmentRefs(id, rev, att.digest, attachmentSaved);
          continue;
        }
        var data;
        if (typeof att.data === 'string') {
          // input is assumed to be a base64 string
          try {
            data = pouchdbBinaryUtils.atob(att.data);
          } catch (e) {
            callback(pouchdbErrors.createError(pouchdbErrors.BAD_ARG,
                     'Attachment is not a valid base64 string'));
            return;
          }
          doMD5(docInfo, key, attachmentSaved)(data);
        } else {
          prepareAttachmentForStorage(att.data,
            doMD5(docInfo, key, attachmentSaved));
        }
      }

      function finish() {
        var seq = docInfo.metadata.rev_map[docInfo.metadata.rev];
        /* istanbul ignore if */
        if (seq) {
          // check that there aren't any existing revisions with the same
          // revision id, else we shouldn't do anything

var att = docInfo.data._attachments[key];

        if (att.stub) {
          // still need to update the refs mapping
          var id = docInfo.data._id;
          var rev = docInfo.data._rev;
          saveAttachmentRefs(id, rev, att.digest, attachmentSaved);
          continue;
        }
        var data;
        if (typeof att.data === 'string') {
          // input is assumed to be a base64 string
          try {
            data = pouchdbBinaryUtils.atob(att.data);
          } catch (e) {
            callback(pouchdbErrors.createError(pouchdbErrors.BAD_ARG,
                     'Attachment is not a valid base64 string'));
            return;
          }
          doMD5(docInfo, key, attachmentSaved)(data);
        } else {
          prepareAttachmentForStorage(att.data,
            doMD5(docInfo, key, attachmentSaved));
        }
      }

      function finish() {
        var seq = docInfo.metadata.rev_map[docInfo.metadata.rev];
        /* istanbul ignore if */
        if (seq) {
          // check that there aren't any existing revisions with the same
          // revision id, else we shouldn't do anything