az network application-gateway ssl-profile add adds a default ssl-policy even though none was selected

**Describe the bug**
When adding a new ssl-profile and not specifying anything for policy-type or policy-name the resulting profile uses one of the predefined policies like "AppGwSslPolicy20150501" instead of a null.

**To Reproduce**
az network application-gateway ssl-profile add --output none `
--gateway-name $wafName `
--resource-group $wafRG `
--name $sslProfileName `

**Expected behavior**
The policy should be created with the "sslPolicy" property value of "null". Otherwise, from the CLI, there is no way of creating a policy with a "null" sslPolicy property so that it uses the default one set in Listeners.

**Environment summary**
I get the same result from a local AZ CLI verison 2.35.0 or from an Azure hosted devops pipeline with the CLI task.