Cannot read property 'length' of null in _updateTaskCount #643
Description
When trying to add Bing maps to an Angular 2 and 4 app, the map freezes the second time you try to zoom.
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[ ] feature request
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Zone.js version: 0.7.7 and 0.7.6
Current behavior
Throws error and freezes the second time the map is zoomed (either by clicking the zoom button or scrolling).
Expected behavior
The map should continue to zoom.
Minimal reproduction of the problem with instructions
The issue can be seen at https://plnkr.co/edit/xF2rtWHPWyf4KcRdihzs?p=preview. After the map loads, click the zoom button (in or out) twice. The first time it zooms properly, the second time it throws an error and freezes. If using the scroll wheel, zoom once and allow the map to stop. Then scroll again to see the error.
The error is thrown in _updateTaskCount. The zoneDelegates variable is null when it's length is checked. I know a check could be wrapped around that for loop, but I'm not sure what the implications of that would be.
