Code Analysis - Rule 4602 and null

In the following procedure declaration:

procedure testing (
p_first in varchar2(10)
,p_second in varchar2(10) default null
) is

the null is marked as violating rule 4602 (Avoid use of literals in non-declarative parts of the program). I think the rule is wrong in this case.

Is there any way to prevent the rule from flagging this and still have it enabled? No parts of this rule seem to be editable. I’m using Toad for Oracle v11.0.0.116.