// If the block at the head of the list in this generation
// is less than 3/4 full, then use it as a todo block.
- if (isPartiallyFull(stp->blocks))
+ if (stp->blocks && isPartiallyFull(stp->blocks))
{
ws->todo_bd = stp->blocks;
ws->todo_free = ws->todo_bd->free;