clustering markers as documented throws a cannot read undefined 'range'

[sdetweil]

from the doc

<template>
  <GMapMap :center="center" :zoom="7" map-type-id="terrain" style="width: 500px; height: 300px">
    <GMapCluster>
      <GMapMarker
        :key="index"
        v-for="(m, index) in markers"
        :position="m.position"
        :clickable="true"
        :draggable="true"
        @click="center = m.position"
      />
    </GMapCluster>
  </GMapMap>
</template>

so it appears there is doc missing on the properties required for GMapCluster