How to check if ViewBag property is null or not exists

I have a requirement to execute a script in document.ready function if viewbag property is null or not exists. Below is the code I wrote to check if viewbag property not exists.

I used recommned approached where you @ViewBag.Property!=null but when I do that I get an error saying name property does not exist in current context,

@section scripts {

@if ((bool)ViewData.ContainsKey("FormSubmitFlag") == false)
{
    <script type="text/javascript">
        $(document).ready(function () {

            var pageVisitCount = sessionStorage.getItem("personalDetailsVisitCount");
            if (pageVisitCount == null) {
                $("#personal-details-form").trigger('reset');
                sessionStorage.setItem("personalDetailsVisitCount", "1");
            }
            else {
                var validator = $("#personal-details-form").validate();
                validator.form();
                cat.personaldetails.validate();
            }
        });
    </script>
}
 
}

Thank you

You can check for null and execute your script.

@if (ViewBag.YourKey== null)
{
 //your code   
}

This will check that ViewBag.YourKey is null if you want to check it for not null you can change the if condition.