toString method
A string representation of this object.
Some classes have a default textual representation,
often paired with a static parse function (like int.parse).
These classes will provide the textual representation as
their string representation.
Other classes have no meaningful textual representation
that a program will care about.
Such classes will typically override toString to provide
useful information when inspecting the object,
mainly for debugging or logging.
Implementation
@override
String toString() {
  return 'CouldNotRollBackException: $exception. \n'
      'For context: The transaction was rolled back because of $cause, which '
      'was thrown here: \n$originalStackTrace';
}