My actionContext is null when called in using Swagger

I have application that uses model validation using OnActionExecuting method.

public override void OnActionExecuting(HttpActionContext actionContext)
            if (!actionContext.ModelState.IsValid)
                actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.BadRequest, GetModelStateErrorMessages(actionContext));

My problem here is that always actionContext values are null. I am calling the API using swagger. enter image description here

My controller section is as follows :

    public string SendEmailToCustomerAPI(GeneralData emailAddress)
        string stat = "";

Swagger screen : enter image description here

Any help is greatly appreciated.

Thank you. PG