rollbar.js: Uncaught TypeError: Cannot set property 'impl' of null

I’m not sure what the exact repro conditions for this error is, as it didn’t seem to be breaking consistently everywhere our code was used. We had previously been using an older version of the JS Rollbar snippet:

var _rollbarConfig = {
    accessToken: "<%=ROLLBAR_ACCESS_TOKEN%>",
    captureUncaught: false,
    payload: {
        environment: "<%=ENVIRONMENT%>"
    }
};
!function(a,b){function c(b){this.shimId=++h,this.notifier=null,this.parentShim=b,window.logger=function(){},a.console&&void 0===a.console.shimId&&(window.logger=a.console.log)}function d(b,c,d){!d[4]&&a._rollbarWrappedError&&(d[4]=a._rollbarWrappedError,a._rollbarWrappedError=null),b.uncaughtError.apply(b,d),c&&c.apply(a,d)}function e(b){var d=c;return g(function(){if(this.notifier)return this.notifier[b].apply(this.notifier,arguments);var c=this,e="scope"===b;e&&(c=new d(this));var f=Array.prototype.slice.call(arguments,0),g={shim:c,method:b,args:f,ts:new Date};return a._rollbarShimQueue.push(g),e?c:void 0})}function f(a,b){if(b.hasOwnProperty&&b.hasOwnProperty("addEventListener")){var c=b.addEventListener;b.addEventListener=function(b,d,e){c.call(this,b,a.wrap(d),e)};var d=b.removeEventListener;b.removeEventListener=function(a,b,c){d.call(this,a,b&&b._wrapped?b._wrapped:b,c)}}}function g(a,b){return b=b||window.logger,function(){try{return a.apply(this,arguments)}catch(c){b("Rollbar internal error:",c)}}}var h=0;c.init=function(a,b){var e=b.globalAlias||"Rollbar";if("object"==typeof a[e])return a[e];a._rollbarShimQueue=[],a._rollbarWrappedError=null,b=b||{};var h=new c;return g(function(){if(h.configure(b),b.captureUncaught){var c=a.onerror;a.onerror=function(){var a=Array.prototype.slice.call(arguments,0);d(h,c,a)};var g,i,j=["EventTarget","Window","Node","ApplicationCache","AudioTrackList","ChannelMergerNode","CryptoOperation","EventSource","FileReader","HTMLUnknownElement","IDBDatabase","IDBRequest","IDBTransaction","KeyOperation","MediaController","MessagePort","ModalWindow","Notification","SVGElementInstance","Screen","TextTrack","TextTrackCue","TextTrackList","WebSocket","WebSocketWorker","Worker","XMLHttpRequest","XMLHttpRequestEventTarget","XMLHttpRequestUpload"];for(g=0;g<j.length;++g)i=j[g],a[i]&&a[i].prototype&&f(h,a[i].prototype)}return a[e]=h,h},h.logger)()},c.prototype.loadFull=function(a,b,c,d){var e=g(function(){var a=b.createElement("script"),e=b.getElementsByTagName("script")[0];a.src=d.rollbarJsUrl,a.async=!c,a.onload=f,e.parentNode.insertBefore(a,e)},window.logger),f=g(function(){if(void 0===a._rollbarPayloadQueue)for(var b,c,d,e,f=new Error("rollbar.js did not load");b=a._rollbarShimQueue.shift();)for(d=b.args,e=0;e<d.length;++e)if(c=d[e],"function"==typeof c){c(f);break}},window.logger);g(function(){c?e():a.addEventListener?a.addEventListener("load",e,!1):a.attachEvent("onload",e)},window.logger)()},c.prototype.wrap=function(b){try{if("function"!=typeof b)return b;if(b._isWrap)return b;if(!b._wrapped){b._wrapped=function(){try{return b.apply(this,arguments)}catch(c){throw a._rollbarWrappedError=c,c}},b._wrapped._isWrap=!0;for(var c in b)b.hasOwnProperty(c)&&(b._wrapped[c]=b[c])}return b._wrapped}catch(d){return b}};for(var i="log,debug,info,warn,warning,error,critical,global,configure,scope,uncaughtError".split(","),j=0;j<i.length;++j)c.prototype[i[j]]=e(i[j]);var k="//d37gvrvc0wt4s1.cloudfront.net/js/v1.1/rollbar.min.js";_rollbarConfig.rollbarJsUrl=_rollbarConfig.rollbarJsUrl||k;var l=c.init(a,_rollbarConfig);l.loadFull(a,b,!1,_rollbarConfig)}(window,document);

which was throwing the error referenced in https://github.com/rollbar/rollbar.js/issues/98. And while we weren’t double-loading Rollbar (in so far as rollbar.min.js was only ever requested once), as far as I could make out from the latest minified snippet on https://rollbar.com/docs/notifier/rollbar.js/, there now seem to be some NPE guards, so we tried updating to the latest, only to get reports of the error mentioned in the title.