_Im_NetworkSession_AzureFirewallV02 parser failing

**Describe the bug**
I have come across an issue with the "_Im_NetworkSession_AzureFirewallV02" parser failing in some workspaces: https://github.com/Azure/Azure-Sentinel/blob/3a38a5abe67274b30d672d081d273a512034f28e/Parsers/ASimNetworkSession/Parsers/vimNetworkSessionAzureFirewall.yaml

In some workspaces that do not ingest AzureDiagnostics, it is failing with the error :
"'where' operator: Failed to resolve scalar expression named 'msg_s'"

Adding the line "| extend msg_s = column_ifexists("msg_s", "")" within the AzureDiagnostics logic seems to resolve the issue:

**To Reproduce**
Steps to reproduce the behavior:
1. Go to a workspace that ingests data through one of the other means, but not AzureDiagnostics, e.g. AZFWNetworkRule, AZFWNatRule, AZFWIdpsSignature or AZFWThreatIntel
2. Run the _Im_NetworkSession_AzureFirewallV02 parser function
3. See error

**Expected behavior**
The parser should run successfully, regardless of the logic within the AzureDiagnostics section, if the customer does not ingest the table.