ReferenceError: markers_ is not defined

[sompylasar]

Uncaught ReferenceError: markers_ is not defined
Cluster.updateIcon @ markerclusterer.js:1015
Cluster.addMarker @ markerclusterer.js:880
MarkerClusterer.addToClosestCluster_ @ markerclusterer.js:764
MarkerClusterer.createClusters_ @ markerclusterer.js:788
MarkerClusterer.redraw @ markerclusterer.js:709
(anonymous function) @ markerclusterer.js:174
_.H.trigger @ js:85
(anonymous function) @ map.js:13
_.H.trigger @ js:85
rb @ js:33
_.t.set @ js:87
Oz.R @ map.js:34

https://github.com/googlemaps/js-marker-clusterer/blob/gh-pages/src/markerclusterer.js#L1015

Repro at https://googlemaps.github.io/js-marker-clusterer/examples/simple_example.html