throws error if transcluded content undefined #932
Description
If the component <comp> uses <content> in its template and no cnotents embed in the <comp>, the comipler will throw error. For example [demo (See error in the console)]:
<div id='app'><comp></comp></div>new Vue({
el: '#app',
components: {
comp: {
replace: true,
template: '<div><content></content></div>'
}
}
})This issue only raises up after the commit for refactor content transclusion.