"TypeError: popover is null" issue in firefox (with solution)

[OneOfTheWorld]

Branch: master
Error description:
<div class="cntr-flag" v-if="!isUseDefaultCost"> <tooltip effect="scale" placement="left" trigger="click"> <div slot="content" style="width: 150px;"> Container Size/Type: {{cntrSizeType}} </div> <div class="cntr-rotate"> {{cntrSizeType}} </div> </tooltip> </div>
as the above code, I want to use Tooltip.vue to show some tips to user, but found that
In chrome, the tooltip can always show rightly, but in firefox the tooltip sometimes can not show rightly:
Right one:

Wrong one:

and the console output the following error:

[OneOfTheWorld]

Reason:
Issue file: vue-strap/src/Tooltip.vue

<div v-el:popover v-if="show" style="display:block;"
    :class="['tooltip',placement]"
    :transition="effect"

Issue file: vue-strap/src/utils/popoverMixins.js

toggle (e) {
      if (e && this.trigger === 'contextmenu') e.preventDefault()
      if (!(this.show = !this.show)) { return }
      setTimeout(() => {
        const popover = this.$els.popover
        const trigger = this.$els.trigger.children[0]
        switch (this.placement) {
          case 'top' :
            this.position.left = trigger.offsetLeft - popover.offsetWidth / 2 + trigger.offsetWidth / 2
            this.position.top = trigger.offsetTop - popover.offsetHeight
            break
.........

when call toggle function, once set the "this.show = true", then the VUE will take time to render the popover div , but In firefox the setTimeout may execute before the popover div rendered, so it will cause the popover el null error.

[OneOfTheWorld]

Solution
Target File: vue-strap/src/utils/popoverMixins.js

in toggle function, change setTimeout function to the following:

Vue.nextTick(() => {
  const popover = this.$els.popover
  const trigger = this.$els.trigger.children[0]
  switch (this.placement) {
    case 'top' :
      this.position.left = trigger.offsetLeft - popover.offsetWidth / 2 + trigger.offsetWidth / 2
      this.position.top = trigger.offsetTop - popover.offsetHeight
      break
    case 'left':
      this.position.left = trigger.offsetLeft - popover.offsetWidth
      this.position.top = trigger.offsetTop + trigger.offsetHeight / 2 - popover.offsetHeight / 2
      break
    case 'right':
      this.position.left = trigger.offsetLeft + trigger.offsetWidth
      this.position.top = trigger.offsetTop + trigger.offsetHeight / 2 - popover.offsetHeight / 2
      break
    case 'bottom':
      this.position.left = trigger.offsetLeft - popover.offsetWidth / 2 + trigger.offsetWidth / 2
      this.position.top = trigger.offsetTop + trigger.offsetHeight
      break
    default:
      console.warn('Wrong placement prop')
  }
  popover.style.top = this.position.top + 'px'
  popover.style.left = this.position.left + 'px'
});