Unable to deploy MPE to private link service ( ` groupid = "" ` )

We recently introduced a MPE pointing to a private link service (to a load balancer in front of AKS).
The MPE definition looks like this in git:
```json
{
"name": "my-mpe",
"properties": {
"privateLinkResourceId": "/subscriptions//resourceGroups//providers/Microsoft.Network/privateLinkServices/",
"groupId": "",
"fqdns": [
"myfqdn.example.com"
]
}
}
```
When trying to deploy this mpe, I get the error
```
"StatusCode":400,"Message":"Invalid Request"
```
____
I suspect this might be because of parsing/validation of the `groupId` (which is in fact correct, and needs to be empty)?