code: function omitFieldsToMongo(omitFields) {
      if (!omitFields) return null
      var hash = {}
      omitFields.split(',').forEach(function(omitField) {
          hash[omitField.trim()] = 0
      })
      return hash
  }
docs: Convert comma separated list to a mongo projection which specifies fields to omit. for example f('field2') -> {field2:false}