MediaPlayerService: allow next player to be NULL am: 2828412787 am: f4e00a7c5a am: 0dd714e408 am: de97dbd662 am: a7549d3dce am: c6fdb3d696 am: 629e78c10f am: 50b9d889e6 am: 81e0557519
am: 31407677bc

Change-Id: I0dba90208e5a8f316658e3521544445fa00614cc