Which could mean the PID was either too short-lived for Lsof to find any open fd's or it didn't use any fd's?
Say (stupid example) you would want to find fd's zero to hundred for all instances of Apache. You could get a list of pids, knowing Apache is called "httpd", and feed it to xargs which in turn will run lsof:
pgrep -f httpd|xargs -iP lsof -d 0-100 -a -p 'P'
Likewise you can do for any app you're wanting to find fd's for.