CorePageApp Exception: The null object does not have a method 'open'

Question

I am running an app with DartEditor (not dart-eclipse plugin)

Dart Editor version 1.10.0.dev_01_01 (DEV)
Dart SDK version 1.10.0-dev.1.1

I am consistently getting the following when the app is executed

Exception: The null object does not have a method 'open'.

NoSuchMethodError: method not found: 'open'
Receiver: null
Arguments: [] (package:polymer_snippet/material_design/core_page`/core_page_app.dart:41)`

The offending open() is the last line in the CarePageApp attached() method below:

 @override
  void attached()
  {
    super.attached();
    pfm = $['pfm'] as PaperFabMenu ;
    pfm.open(); // pfm seems to be null

  }

Any help is appreciated.

Thanks

NB: There is no specific code for me to attach.