It has been announced, and related documentations have been updated or published.
> What's up with the change to the Python API for nulls in Build 14252?
> How does FME handle null attribute values?
> FME 2014 Null Porting Guide for Plug-ins
I updated these articles in this blog.
> Default Attribute Names of XLSXR in FME 2014
> Null in FME 2014: Handling Null with Python / Tcl
> Efficiency of List Attribute Manipulation with Python
In short, when specified attribute stores <null>, FMEFeature.getAttribute method returns
None in FME 2014 (without SP*),
an empty string in FME 2014 SP1+ (build 14252 or later).