Public IP's PTR record cannot be removed by CLI

I was following this doc to remove a PTR record that set for public IP
https://docs.microsoft.com/en-us/azure/dns/dns-reverse-dns-for-azure-services#azure-cli-3

> az network public-ip update --resource-group MyResourceGroup --name PublicIp --reverse-fqdn ""

However, following syntax error was returned.
```
az network public-ip update --resource-group bootcampdb --name VM01-ip --reverse-fqdn ""
argument --reverse-fqdn: expected one argument

TRY THIS:
az network public-ip update --resource-group MyResourceGroup --name MyIp --dns-name MyLabel --allocation-method Static
Update a public IP resource with a DNS name label and static allocation.

az network public-ip list
List all public IPs in a subscription.

az network public-ip list --resource-group MyResourceGroup
List all public IPs in a resource group.

https://docs.microsoft.com/en-US/cli/azure/network/public-ip#az_network_public_ip_list
Read more about the command in reference docs
```

I was able to do this using following PowerShell command
https://docs.microsoft.com/en-us/azure/dns/dns-reverse-dns-for-azure-services#azure-cli-3
```
PS /home/bang> $pip = Get-AzPublicIpAddress -Name "VM01-ip" -ResourceGroupName "bootcampdb"
PS /home/bang> $pip.DnsSettings.ReverseFqdn = ""
PS /home/bang> Set-AzPublicIpAddress -PublicIpAddress $pip

Name : VM01-ip
ResourceGroupName : bootcampdb
Location : japaneast
Id : /subscriptions/00ad8164-fccc-4682-912a-966610f3d064/resourceGroups/bootcampdb/providers/Microsoft.Network/publicIPAddresses/VM01-ip
Etag : W/"8af51b91-cade-45d5-996d-2e69fd4c5db4"
ResourceGuid : 43a61d14-cd1d-472f-8b36-5a24dcf242aa
ProvisioningState : Succeeded
Tags :
PublicIpAllocationMethod : Static
IpAddress : 20.44.176.182
PublicIpAddressVersion : IPv4
IdleTimeoutInMinutes : 4
IpConfiguration : {
"Id": "/subscriptions/00ad8164-fccc-4682-912a-966610f3d064/resourceGroups/bootcampdb/providers/Microsoft.Network/networkInterfaces/vm01-win2016396/ipConfigurations/ipconfig1"
}
DnsSettings : {
"DomainNameLabel": "vm01-bootcampdb",
"Fqdn": "vm01-bootcampdb.japaneast.cloudapp.azure.com",
"ReverseFqdn": ""
}
Zones : {}
Sku : {
"Name": "Basic",
"Tier": "Regional"
}
IpTags : []
ExtendedLocation : null
```

So looks like there's either a typo in Doc or bug in CLI, can someone look into this?