@VisibleForTesting public Block createNextBlock(Address to,long time){
  return createNextBlock(to,null,time,EMPTY_BYTES,Utils.toNanoCoins(50,0));
}

@ VisibleForTesting public Block createNextBlock ( Address to , long time ) { return createNextBlock ( to , null , time , EMPTY_BYTES , Utils . toNanoCoins ( 50 , 0 ) ) ; }
returns a solved block that builds on top of this one . this exists for unit tests .
