save() starts by this:

if ( obj == null || typeof( obj ) == "undefined" )
throw "can't save a null";

This is apparently to catch both null and undefined.

However, since the first check only uses == instead of ===, it matches undefined, and the second part of the check is never used. This could be improved in one of two ways:

• drop the second part of the check since it is unused anyway:
  if ( obj == null)
  throw "can't save a null";
• use an identical check for null
  if ( obj === null || typeof( obj ) == "undefined" )
  throw "can't save a null";