code: function fieldsToMongo(fields) {
      if (!fields) return null
      var hash = {}
      fields.split(',').forEach(function(field) {
          hash[field.trim()] = 1
      })
      return hash
  }
docs: Convert comma separated list to a mongo projection. for example f('field1,field2,field3') -> {field1:true,field2:true,field3:true}