TypeError thrown when adding/removing ripple from DOM

[ronnyroeller]

Description

Rolling back to paper-ripple 1.0.5 solves the problem, i.e. it was introduced in 1.0.6.

The keyEventTarget is set to null when the ripple is removed from the DOM. Adding the ripple back to the DOM causes the following error in the console:

error TypeError: Cannot read property 'addEventListener' of null
    at paper-ripple.<anonymous> (https://polygit.org/components/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html:404:30)
    at Array.forEach (native)
    at paper-ripple._listenKeyEventListeners (https://polygit.org/components/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html:398:40)
    at paper-ripple.attached (https://polygit.org/components/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html:298:14)
    at paper-ripple._invokeBehavior (https://polygit.org/components/polymer/polymer-micro.html:433:4)
    at paper-ripple._doBehavior (https://polygit.org/components/polymer/polymer-micro.html:426:6)
    at https://polygit.org/components/polymer/polymer-micro.html:210:6
    at Object.whenReady (https://polygit.org/components/polymer/polymer-micro.html:103:1)
    at paper-ripple.attachedCallback (https://polygit.org/components/polymer/polymer-micro.html:208:22)
    at paper-ripple.attachedCallback (https://polygit.org/components/polymer/polymer-mini.html:104:22)

Now, removing the ripple again from the DOM causes this error:

error TypeError: Cannot read property 'removeEventListener' of null
    at paper-ripple._unlistenKeyEventListeners (https://polygit.org/components/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html:421:25)
    at paper-ripple.detached (https://polygit.org/components/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html:302:14)
    at paper-ripple._invokeBehavior (https://polygit.org/components/polymer/polymer-micro.html:433:4)
    at paper-ripple._doBehavior (https://polygit.org/components/polymer/polymer-micro.html:426:6)
    at https://polygit.org/components/polymer/polymer-micro.html:217:6
    at Object.whenReady (https://polygit.org/components/polymer/polymer-micro.html:103:1)
    at paper-ripple.detachedCallback (https://polygit.org/components/polymer/polymer-micro.html:215:22)
    at Object.removeChild (https://polygit.org/components/polymer/polymer-mini.html:568:26)
    at Object.removeChild (https://polygit.org/components/polymer/polymer-mini.html:775:18)
    at dom-bind.scope.toggle (https://null.jsbin.com/runner:9:37)

Expected outcome

Ripple can be added and remove from the DOM without throwing errors in the console.

Actual outcome

Live Demo

https://jsbin.com/kowecehexi/edit?html,output

Steps to reproduce

1. Open JSbin
2. Open browser console
3. Click [hide] button
4. Click [show] button