code: 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;
  }
docs: @license
  Copyright Google Inc. All Rights Reserved.
  
  Use of this source code is governed by an MIT-style license that can be
  found in the LICENSE file at https://angular.io/license
   
  @param {?} previousStyles
  @param {?} newStyles
  @param {?=} nullValue
  @return {?}