HTTP error

I was getting the below error all the time.
git clone https://github.com/prateek/nifi-parcel.git
Initialized empty Git repository in /etc/nifi-parcel/.git/
error:  while accessing https://github.com/prateek/nifi-parcel.git/info/refs

fatal: HTTP request failed

can you explain pre requisite step as well clearly?
Thanks.