push: error in browser console after push enabled/disabled

Cloned from RF-13949. The original issue was not resolved in scope of RF 4.5.3. The fix was accidently removed by RF-13975 (upgrade Atmosphere to 2.2.4 and Atmosphere JS to 2.2.6) (commit).

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Original Description:

There is an error in console in Firefox after the push is enabled or disabled. The push is working even with this error, but it makes problems in Selenium tests (RFPL-3692).

The error: no element found @ __richfaces_push:1

Could be reproduced in Metamer:

1. deploy metamer and open http://localhost:8080/metamer/faces/components/a4jPush/twoPushCDI.xhtml
2. open console (F12, note: the error is not displayed in Firebug)
3. click on the "enabled" checkbox right next to the "Push 1!" button.