public void Execute()
{
int cnt = 1;
var task = new VariableArgumentTask<int> (2, (a) => cnt += a.Length);
try {
task.Execute ();
Assert.Fail ("#1");
} catch (NullReferenceException) {}
task [0] = new PortElement<int> (10);
try {
task.Execute ();
Assert.Fail ("#2");
} catch (NullReferenceException) {}
task [1] = new PortElement<int> (20);
Assert.IsNull (task.Execute (), "#3");
Assert.AreEqual (3, cnt, "#4");
}