Describe the bug

Azure Key Vault creation using az keyvault gives an error when soft delete is disabled and does not create the key vault.

To Reproduce

Running the following command

az keyvault create --resource-group myrg --name mykv \
  --location westeurope --sku standard --enable-soft-delete false

returns

The property "enableSoftDelete" must be set to true.

Expected Behavior

Should create the key vault with soft delete disabled.

Environment summary

OS Name: Microsoft Windows 10 Pro OS Version: 10.0.17763 N/A Build 17763

az --version
azure-cli                          2.5.0

command-modules-nspkg              2.0.3
core                               2.5.0
nspkg                              3.0.4
telemetry                          1.0.4

Same error also in Cloud Shell environment.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.6 LTS
Release:        16.04
Codename:       xenial

$ az --version
azure-cli                          2.4.0 *

command-modules-nspkg              2.0.3
core                               2.4.0 *
nspkg                              3.0.4
telemetry                          1.0.4

Extensions:
application-insights               0.1.6
resource-graph                     1.0.0
azure-devops                      0.18.0

Additional Context

The reason seems to be the property softDeleteRetentionInDays in the JSON payload the az keyvault command sends to the REST API.

{
    "location": "westeurope",
    "properties": {
        "tenantId": "<removed>",
        "sku": {
            "family": "A",
            "name": "standard"
        },
        "accessPolicies": [],
        "enableSoftDelete": false,
        "softDeleteRetentionInDays": 90

      // rest of the properties removed
    }
}

Everything seems to work correctly if the key vault creation is invoked directly using the az rest command and without the property softDeleteRetentionInDays in the JSON payload.

{
    "location": "westeurope",
    "properties": {
        "tenantId": "<removed>",
        "sku": {
            "family": "A",
            "name": "standard"
        },
        "accessPolicies": [],
        "enableSoftDelete": false,
        "enableRbacAuthorization": false
    }
}

az rest \
    --method PUT \
    --uri "https://management.azure.com/subscriptions/<removed>/resourceGroups/my-resource-group/providers/Microsoft.KeyVault/vaults/my-keyvault?api-version=2019-09-01"
    --header Content-Type=application/json \
    --body <the json playload above>