AccessPolicies is not required in swagger but still need pass empty array

In the [swagger definition](https://github.com/Azure/azure-rest-api-specs/blob/main/specification/keyvault/resource-manager/Microsoft.KeyVault/stable/2021-10-01/keyvault.json#L1219) of keyVault, accessPolicies is not a required parameter. But the test result showed that we at least need to pass an empty array to make this request work. I don't think it's a ideal behavior because if the property is not required, we should be able to create the vault without extra operations such as passing an empty array.

Considering this problem was found in .net sdk, also created an issue in azure-sdk-for-net repo, see more details [here](https://github.com/Azure/azure-sdk-for-net/issues/28677).