Azure Front Door Update WAF Policy fails with BadRequest due to malformed AttackerIP (Block-IPAzureWAF v2)

**Describe the bug**
Block-IPAzureWAF v2 Sentinel Playbook

The AttackerIP variable contains a malformed IP address, causing the Update WAF Policy block to fail due to a BadRequest on the WAF policy.

**Reproduce**
Steps to reproduce the behavior:
1. Deploy the Block-IPAzureWAF playbook with Azure Front Door Resource Id
2. Open an alert and run the playbook
3. See BadRequest error in "Update WAF Policy"

**Expected behavior**
The AttackerIP variable contains a valid IP address when passed to the request to update the WAF policy.

**Environment- if applicable**
- Azure Front Door WAF

**Logs- if applicable**
Real IP address replaced with mock address.

```
"matchConditions": [
{
"matchValue": [
"null123.123.123.123"
],
```
...

```
{
"error": {
"code": "BadRequest",
"message": "WebApplicationFirewallPolicy validation failed. More information \"Value null123.123.123.123 is not a valid IP Address in rule SentinelBlockIP\"."
}
}

```

**Additional context**
We worked around this issue by editing the playbook and changing the initial value of the AttackerIP variable from "null" to "".