The stack trace from where the exception was thrown (as opposed to where it was caught).
StackTrace objects are opaque except for their toString function.
If this field is not null, then the stackFilter callback, if any, will
be called with the result of calling toString on this object and
splitting that result on line breaks. If there's no stackFilter
callback, then FlutterError.defaultStackFilter is used instead. That
function expects the stack to be in the format used by
final StackTrace stack