RTCP:Can a sender sender reception report blocks in an SR packet for recievers for which it hasn't recieved any RTP data?

Hi
I've been going thru the RTP specs for the last couple of days,but am
unable to find an answer to this doubt of mine. Say u have two
participants capable of 2 way RTP communication, but it just happens
A sends RTP packets and B just recieves them. Now when A generates it's

SR , will it also append a reception report block for B with an LSR
=0.Or will there just be an SR with 0 report blocks. I feel there has
to be a report block with LSR=0. Could someone please clarify this
doubt??

Thanks !
Jon

jon wayne