I‘m using portmaster to manage my ports without external databases. However, when I run the try to run pkg_version -l ‘<', I'm getting the following error:

pkg_version: corrupted record (pkgdep line without argument), ignoring

How do I fix this problem?

You can fix this problem running the following commands:
portmaster --check-depends
After that run usual portmaster -Da command:
# portmaster -Da
However, as noted here, it is good idea to get list of ports first:

cd /var/db/
cp -Rp pkg pkg-before
portmaster --check-depends
diff -ur pkg-before pkg > ~/pkg-dir.diff1
cp -Rp pkg pkg-after
portmaster --check-depends
diff -ur pkg-after pkg > ~/pkg-dir.diff2
cd pkg
egrep -l '(pkgdep$|pkgdep $)' */+CONTENTS > ~/pkg-dir.egrep

See portmaster man page for more information.