nullref after reload -> save on "previousContentObject"

Hi,
I encountered a nullref in ink on this line: (ink 1.1.1)
https://github.com/inkle/ink/blob/master/ink-engine-runtime/CallStack.cs#L145

I was reloading a state after changing the ink scripts, and the previous "previousContentObject" was pointing to a stitch I had renamed.
The weird thing is that I had no problems loading this state, but I got a crash when trying to save again, immediately after loading. (I do that as a kind of "automatic testing" of my game serialization).
It looks like can avoid the crash just with adding a null check, like in the snippet below , my question is: how is this "previousContentObject" used ? Which problems should I expect from just ignoring this error?

```
if (!previousPointer.isNull)
{
var path = previousPointer.Resolve()?.path?.ToString();
if (path != null)
{
writer.WriteProperty("previousContentObject", path);
}
else
{
// Question: should we expect further problems ??
}
}
```
Thanks for your help, and thanks for this great lib!!