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() {
  final buffer = StringBuffer();
  final exceptionType = runtimeType.toString();
  buffer.write(exceptionType);
  if (message != null) {
    buffer.write(": $message");
  }
  if (stackTrace != null) {
    buffer.writeln();
    _printStackTrace(buffer, exceptionType, stackTrace!);
  }
  if (innerException != null) {
    if (innerException is AppException) {
      buffer.writeln("Caused by: $innerException");
    } else {
      buffer.write("Caused by: $innerException\n");
      if (innerStackTrace != null) {
        _printStackTrace(buffer, exceptionType, innerStackTrace!);
      }
    }
  }
  return buffer.toString();
}