Minimal. We weren't 'expecting' anything, but half the damned obstacles we run into aren't exactly planned. Most asteroids qualify as dark matter if they're far enough away from a heliosphere. Ship can't pick them all out of the dark in the nebula.

[Maybe they'd get lucky...]

Good news. There's a lot more empty space out there than asteroids. A LOT more of it. Bad news? We've got shit luck.