What I need:
Get access to the Internet Message Id for an email related incident via the Microsoft Graph Security API
My problem:
I used Outlook's reporting module and marked an email that was in my inbox as Phishing. This then created an event in https://security.microsoft.com. See the below image. Incident ID 16. 
I put together a webhook that is able to pull alerts via the Microsoft Graph Security API. From this call I managed to retrieve the alert's ID. I then used that ID to get more information about the alert by using this call: (https://graph.microsoft.com/v1.0/security/alerts/{alert_id})
In the JSON body of the response there's a property called messageSecurityStates that is always empty. I found this link to Javadoc.io where the object's properties are described and it looks like this property should contain the Internet Message Id. But when querying the Microsoft Graph Security API, the object is always empty.
Question:
What do I need to do to ensure that my email related alerts that are queried via the MS Graph Security API have email related information such as Internet Message Id?