the following code from jQuery(1.4.2).fn.extend(  { data : function {.........} } ):

2. if ( typeof key === "undefined" && this.length ) {
3. .....
4. } else if ( typeof key === "object" ) {
5. ......
6. }

does not handle the situation when:  key is undefined,and this.length===0,

next line of code:

1. var parts = key.split(".");

cause the exception because key is undefined.

I think jQuery("does not exist ").data() should return undefined , instead of throwing an exception.