mawk: run time error (make all - Nagios Plugins 2.0.2)

OS: Debian 7.0

When compiling Nagios Plugins 2.0.2 I received an error:

NP_VERSION=2.0.2 mawk -f ./subst > check_mailq
mawk: run time error: regular expression compile failed (missing operand)
/var/lib/postfix' || -d '/var/local/lib/postfix
        FILENAME="" FNR=613 NR=613
make[2]: *** [check_mailq] Error 2
make[2]: Leaving directory `/root/software/nagios-plugins-2.0.2/plugins-scripts'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/root/software/nagios-plugins-2.0.2'
make: *** [all] Error 2

After some research I found out I needed to install mawk (apt-get install mawk).
But not in all cases this worked out for me.

It seems there is an error the code/compiler...
The problem is the compiler cannot parse the "||" regular expression in the if statement.
However, if you change the "||" with "or" everything works fine :-)

Eventually the code is as follows (

        if (defined $opt_M) {
                if ($opt_M =~ /^(sendmail|qmail|postfix|exim|nullmailer)$/) {
                        $mailq = $opt_M ;
                }elsif( $opt_M eq ''){
                        $mailq = 'sendmail';
                        print "-M: $opt_M is not supported\n";
                        exit $ERRORS{'UNKNOWN'};
                if (defined $utils::PATH_TO_QMAIL_QSTAT
                    && -x $utils::PATH_TO_QMAIL_QSTAT)
                        $mailq = 'qmail';
                elsif (-d '/var/lib/postfix' or -d '/var/local/lib/postfix'
                       or -e '/usr/sbin/postfix' or -e '/usr/local/sbin/postfix')
                        $mailq = 'postfix';
                elsif (-d '/usr/lib/exim4' or -d '/usr/local/lib/exim4'
                       or -e '/usr/sbin/exim' or -e '/usr/local/sbin/exim')
                        $mailq = 'exim';
                elsif (-d '/usr/lib/nullmailer' or -d '/usr/local/lib/nullmailer'
                       or -e '/usr/sbin/nullmailer-send'
                       or -e '/usr/local/sbin/nullmailer-send')
                        $mailq = 'nullmailer';
                else {
                        $mailq = 'sendmail';