Why does Google says that an item needs an url property in schema.org? - schema.org

Question

When I put an example from the ItemList page in the Structured Data Testing Tool by Google, it says that an item needs an url property.
The example:
<script type="application/ld+json">
{
"#context": "http://schema.org",
"#type": "ItemList",
"name": "Top 5 covers of Bob Dylan Songs",
"itemListOrder": "http://schema.org/ItemListOrderAscending",
"numberOfItems": 5,
"itemListElement": [
{
"#type": "ListItem",
"position": 5,
"item": {
"#type": "MusicRecording",
"name": "If Not For You",
"byArtist": {
"#type": "MusicGroup",
"name": "George Harrison"
}
}
}
]
}
</script>
I simplified it to have a minimal example, but the error is the same with the exact example from the page.
I tested this code and there is no error here:
{
"#type": "ListItem",
"position": 5,
"item": {
"#type": "MusicRecording",
"name": "If Not For You",
"byArtist": {
"#type": "MusicGroup",
"name": "George Harrison"
}
}
}
Can anybody explain this to me?

Answer 1

A ItemList in general is a list collection of sites like a breadcrumb, overview of bandsites, etc.
If you only want a list without links to deatils sites you can use only ListItem with Items. This is the different of your samples ItemList and ListItem.