nodejs forever: File config.json not found or is invalid

I have strange problem with nodejs forever.

I have cloned iodocs to /home/user/iodocs

If I start forever from iodocs directory:

user@ubuntu:~/iodocs$ forever start app.js

everything is working fine.

If I try start forever from another directory, for example:

user@ubuntu:~$ forever start --sourceDir /home/user/iodocs/ app.js
warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
info:    Forever processing file: app.js

In log file I have seen:

user@ubuntu:~$ forever logs
info:    Logs for running Forever processes
data:        script                      logfile                         
data:    [0] /home/user/iodocs/app.js /home/user/.forever/xYBf.log 
user@ubuntu:~$ cat /home/user/.forever/xYBf.log
File /home/user/config.json not found or is invalid.  Try: `cp config.json.sample config.json`
error: Forever detected script exited with code: 1

Why forever try to read config from unix user home directory instead sourceDir?

How to fix it?