old_contents: /* @flow */
  'use strict';
  module.exports.hello = function(name: string): string {
      return 'Hello, ' + name + '!';
  };
  if(window.console) {
      window.console.log(module.exports.hello('world'));
  }
new_contents: /* @flow */
  'use strict';
  module.exports.hello = function(name: string): string {
      return 'Hello, ' + name + '!';
  };
  if(window && window.console) {
      window.console.log(module.exports.hello('world'));
  }
subject: Add null check