Hello Saif
A summary will be advertised only if there is a subnet that is included within the summary. If that does not exist, then the summary route will not be installed, and no summary LSAs will be sent. Also, no Null0 route will be placed in the routing table. So in this case, the no discard-route internal command would be meaningless.
Now if you have a destination within the summary that has been configured, then a Null0 route will be installed in the routing table and summary LSAs will be sent. This is the normal operation.
Now if you want to remove the Null0 from the routing table, then in the second scenario you can do this with the no discard-route internal command as you mentioned.
An example of where this would be useful can be found in the following Cisco Support community post:
I hope this has been helpful!
Laz