如何检查IMobileServiceTableQuery <T> 是否为空

Question

I want to check if a value exists in my Easy Tables Azure database before inserting it.

var l = App.MobileService.GetTable<User>().Where(u => u.email == user.email)

When I then try to turn the IMobileServiceTableQuery, l into a list I get a NullReferenceException

if(l == null)
{

}
else{
     var list = await l.ToListAsync();
     await App.MobileService.GetTable<User>().InsertAsync(user);
}

When I try the following:

var l = App.MobileService.GetTable<User>().Where(u => u.email == user.email);
        if(l.Query == null)
        {

        }
        else{
            // var list = await l.ToListAsync();
            if(l.Query.Count() == 0)
            {
                await App.MobileService.GetTable<User>().InsertAsync(user);
            }
        }

...The insert is made each time I run the code. Meaning the l.Query.Count() is always 0.

How can see and check if IMobileServiceTableQuery is empty or not?