Gap underneath concrete slab (walkway)

Hi there,

I've noticed that there was gap underneath concrete slab and am not too sure if I need to fill the gap with dirt or something? I assumed it was washed out when it rained hard last week. My concern is the walk way concrete slab will sink or be collapsed due to lack of proper support. Landscaping company is supposed to be out to start working this week and I am just wondering if I need to fix it before landscaping work gets started. Any advice will be much appreciated.

Thank you!