Underscore.js - compact an object just like compact function for array

gistfile1.js

_.mixin({
      capitalize : function(string) {
          return string.charAt(0).toUpperCase() + string.substring(1).toLowerCase();
      },
      compactObject: function(to_clean) {
          _.map(to_clean, function(value, key, to_clean) {
              if (_.isNull(value) || _.isUndefined(value) || (_.isString(value) && _.trim(value).length === 0) || (_.isBoolean(value) && value === false)) {
                  delete to_clean[key];
              }
          });
          return to_clean;
      }
    });