make index produces 0 byte INDEX-11

[Andy Farkas]

Is it because of "no entry for /usr/ports/:lang/perl5.26" ?
What would cause that? Something in my environment? Something
buried in /usr/local?

FreeBSD 11.3-STABLE #0 r350271

root:~ # cat /etc/make.conf
#ALLOW_UNSUPPORTED_SYSTEM=1
#DEFAULT_VERSIONS+= perl5=5.22
WRKDIRPREFIX=/z/work
root:~ # cat /etc/src.conf
cat: /etc/src.conf: No such file or directory
root:~ #
root:~ # cd /usr/
root:/usr # rm -rf ports ; mkdir ports
root:/usr # svnlite co svn://<my.mirrored.svn.repo>/ports/head /usr/ports
...
Checked out revision 507263.
root:/usr # cd ports/
root:/usr/ports # time make index
Generating INDEX-11 - please wait..--- describe.accessibility ---
--- describe.arabic ---
--- describe.archivers ---
...
--- describe.x11-toolkits ---
--- describe.x11-wm ---
make_index: /usr/ports/archivers/atool: no entry for 
/usr/ports/:lang/perl5.26
  Done.
1533.047u 907.912s 8:12.79 495.3%    23786+867k 500780+163017io 13720pf+0w
root:/usr/ports # ls -l INDEX-11
-rw-r--r--  1 root  wheel  0 Jul 25 19:07 INDEX-11
root:/usr/ports #

Any suggestions?

-andyf