max_dump_file_size set to empty string: What effective limit do you get then?

Contrary to documentation it's possible to set max_dump_file_size to empty string: SQL> alter session set max_dump_file_size='';
 
Session altered

This results in value=NULL in
select * from v$parameter where name='max_dump_file_size'

What is really the effective limit in this case?



Strangely enough when using NULL instead it fails:

alter session set max_dump_file_size=null
 
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-04017: invalid value NULL (length = 4) for parameter max_dump_file_size
 
SQL>

Seems like this implicitly instead does a:

SQL> alter session set max_dump_file_size='null';