Logstash since dbpath= null

I am getting this logstash error while running a command.bin/logstash -f /Users/chetatri/Desktop/logstash/csv.conf

and further, I figure out it because of #sincedb_path => "/dev/null" and if I comment this it working else it gave me the error. What happening in the background I don't understand - Can anybody help me to understand. i also wanted to understand how to get logstash plugin and make it work locally and where i can find detail logs of logstash.

Please do not post pictures of text, just post the text.

Thank you . I will do that