docs: function prepareFinalAnimationStyles(previousStyles, newStyles, nullValue) {
      if (nullValue === void 0) { nullValue = null; }
      var /** @type {?} */ finalStyles = {};
      Object.keys(newStyles).forEach(function (prop) {
          var /** @type {?} */ value = newStyles[prop];
          finalStyles[prop] = value == AUTO_STYLE ? nullValue : value.toString();
      });
      Object.keys(previousStyles).forEach(function (prop) {
          if (!isPresent(finalStyles[prop])) {
              finalStyles[prop] = nullValue;
          }
      });
      return finalStyles;
  }