Omit null value in CLI output.

**Is your feature request related to a problem? Please describe.**

CLI outputs all properties defined in swagger model definition although it is not returned in response. We can see some "null"s in final output. More than one customers reported it is confusing. They want to remove them.

Example
```
Response content:
{
"name": "vm1",
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Compute/virtualMachines/vm1",
"type": "Microsoft.Compute/virtualMachines",
"location": "eastasia",
"tags": {},
"properties": {
"vmId": "00000000-0000-0000-0000-000000000000",
"hardwareProfile": {
"vmSize": "Standard_DS1_v2"
},
"storageProfile": {
"imageReference": {
"publisher": "Canonical",
"offer": "UbuntuServer",
"sku": "18.04-LTS",
"version": "latest",
"exactVersion": "18.04.202007290"
},
"osDisk": {
"osType": "Linux",
"name": "vm1_OsDisk_1_53a437614cfa458fa68ab0c7b28f5765",
"createOption": "FromImage",
"caching": "ReadWrite",
"managedDisk": {
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/FYVM/providers/Microsoft.Compute/disks/vm1_OsDisk_1_53a437614cfa458fa68ab0c7b28f5765"
}
},
"dataDisks": []
},
"osProfile": {
"computerName": "vm1",
"adminUsername": "fey",
"linuxConfiguration": {
"disablePasswordAuthentication": true,
"ssh": {
"publicKeys": [
{
"path": "/home/fey/.ssh/authorized_keys",
"keyData": "ssh-rsa xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n"
}
]
},
"provisionVMAgent": true,
"patchSettings": {
"patchMode": "ImageDefault"
}
},
"secrets": [],
"allowExtensionOperations": true,
"requireGuestProvisionSignal": true
},
"networkProfile": {"networkInterfaces":[{"id":"/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Network/networkInterfaces/vm1VMNic"}]},
"provisioningState": "Succeeded"
},
"resources": [
{
"name": "AzureNetworkWatcherExtension",
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Compute/virtualMachines/vm1/extensions/AzureNetworkWatcherExtension",
"type": "Microsoft.Compute/virtualMachines/extensions",
"location": "eastasia",
"properties": {
"autoUpgradeMinorVersion": true,
"provisioningState": "Succeeded",
"publisher": "Microsoft.Azure.NetworkWatcher",
"type": "NetworkWatcherAgentLinux",
"typeHandlerVersion": "1.4",
"settings": {}
}
}
]
}
CLI output:
{
"additionalCapabilities": null,
"availabilitySet": null,
"billingProfile": null,
"diagnosticsProfile": null,
"evictionPolicy": null,
"extensionsTimeBudget": null,
"hardwareProfile": {
"vmSize": "Standard_DS1_v2"
},
"host": null,
"hostGroup": null,
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Compute/virtualMachines/vm1",
"identity": null,
"instanceView": null,
"licenseType": null,
"location": "eastasia",
"name": "vm1",
"networkProfile": {
"networkInterfaces": [
{
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Network/networkInterfaces/vm1VMNic",
"primary": null,
"resourceGroup": "fyvm"
}
]
},
"osProfile": {
"adminPassword": null,
"adminUsername": "fey",
"allowExtensionOperations": true,
"computerName": "vm1",
"customData": null,
"linuxConfiguration": {
"disablePasswordAuthentication": true,
"patchSettings": {
"patchMode": "ImageDefault"
},
"provisionVmAgent": true,
"ssh": {
"publicKeys": [
{
"keyData": "ssh-rsa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n",
"path": "/home/fey/.ssh/authorized_keys"
}
]
}
},
"requireGuestProvisionSignal": true,
"secrets": [],
"windowsConfiguration": null
},
"plan": null,
"priority": null,
"provisioningState": "Succeeded",
"proximityPlacementGroup": null,
"resourceGroup": "fyvm",
"resources": [
{
"autoUpgradeMinorVersion": true,
"enableAutomaticUpgrade": null,
"forceUpdateTag": null,
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/fyvm/providers/Microsoft.Compute/virtualMachines/vm1/extensions/AzureNetworkWatcherExtension",
"instanceView": null,
"location": "eastasia",
"name": "AzureNetworkWatcherExtension",
"protectedSettings": null,
"provisioningState": "Succeeded",
"publisher": "Microsoft.Azure.NetworkWatcher",
"resourceGroup": "fyvm",
"settings": {},
"tags": null,
"type": "Microsoft.Compute/virtualMachines/extensions",
"typeHandlerVersion": "1.4",
"typePropertiesType": "NetworkWatcherAgentLinux"
}
],
"securityProfile": null,
"storageProfile": {
"dataDisks": [],
"imageReference": {
"exactVersion": "18.04.202007290",
"id": null,
"offer": "UbuntuServer",
"publisher": "Canonical",
"sku": "18.04-LTS",
"version": "latest"
},
"osDisk": {
"caching": "ReadWrite",
"createOption": "FromImage",
"diffDiskSettings": null,
"diskSizeGb": null,
"encryptionSettings": null,
"image": null,
"managedDisk": {
"diskEncryptionSet": null,
"id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/FYVM/providers/Microsoft.Compute/disks/vm1_OsDisk_1_53a437614cfa458fa68ab0c7b28f5765",
"resourceGroup": "FYVM",
"storageAccountType": null
},
"name": "vm1_OsDisk_1_53a437614cfa458fa68ab0c7b28f5765",
"osType": "Linux",
"vhd": null,
"writeAcceleratorEnabled": null
}
},
"tags": {},
"type": "Microsoft.Compute/virtualMachines",
"virtualMachineScaleSet": null,
"vmId": "00000000-0000-0000-0000-000000000000",
"zones": null
}
```

**Describe the solution you'd like**

**Describe alternatives you've considered**

**Additional context**