How to assign EMPTY to PKG_OPTIONS.maildrop ??

[Heron Gallegos <gallegos%csxxi.net.mx@localhost>]

Hello

Does somebody can help me to assign EMPTY to PKG_OPTIONS.maildrop
without modify maildrop/Makefile?

maildrop/Makefile says:
PKG_SUPPORTED_OPTIONS=  authlib
PKG_SUGGESTED_OPTIONS=  authlib
[...]
.if !empty(PKG_OPTIONS:Mauthlib)
CONFIGURE_ARGS+=        --enable-authlib
.  include "../../security/courier-authlib/buildlink3.mk"
.else
CONFIGURE_ARGS+=        --disable-authlib
.endif

I "supose" the follow line assign an empty value (/etc/mk.conf)
PKG_OPTIONS.maildrop=

But...
The output of "make show-options":
Any of the following general options may be selected:
        authlib

These options are enabled by default:
        authlib

These options are currently enabled:
        authlib

You can select which build options to use by setting PKG_DEFAULT_OPTIONS
or PKG_OPTIONS.maildrop.

It seems like PKG_OPTIONS.maildrop have the value of authlib.

I will appreciate any help or comment.
Heron Gallegos
Saltillo Coahuila Mexico