Parser fails on package initialization block

[ChristopheDeClercq]

When I test the parser with following code block it fails to recognize "initialization part" of the package (the last begin null;).

create or replace package body abc
is
a number;

procedure x
is
y number;
begin
a := y;
end;

begin
null;
end;
/

[z0rg]

It seems the problem is in PLSQLParser.g
package_body
: body_key package_name (is_key | as_key)
package_obj_body*
(begin_key seq_of_statements|end_key package_name?)
-> package_name+ package_obj_body* seq_of_statements?
;
Line
(begin_key seq_of_statements|end_key package_name?)
should look like this:
(begin_key seq_of_statements)? end_key package_name?