When running Enforced Hill Climbing independently of the heuristic on a trivial 
PDDL instance where the initial state already satisfies the goal, an assertion 
fails in debug mode because the number of EHC phases is zero.

https://github.com/aibasel/downward/blob/02f3f92f889f61a1f14a72ba934a5cdde274593
3/src/search/search_algorithms/enforced_hill_climbing_search.cc#L246

We discussed this issue both offline and in the PR.

Summary:
The assertion exists because we log the average expansion per EHC phase. This can also lead 
to a planner crash if run in release mode because C++ does not define what happens when you 
divide by zero.

Therefore, we decided to remove logging of this average and the associated assertion. The 
average can still be calculated from the output, as we log both the total number of 
expansions and the EHC phases. Furthermore, it seems that Lab does not parse "Average 
expansions per EHC phase:", which should hopefully avoid parsing issues for experiments.

I commented on the pull request.

Short story: there's a reason why it must be "assert != 0".
The assertion is there because 0 will cause a problem in the following code. (Negative values would not.)

PR: https://github.com/aibasel/downward/pull/267

Easy fix would be to change assert(num_ehc_phases != 0); to assert(num_ehc_phases 
>= 0);

Domain:

(define (domain trivial)
  (:predicates (p))
)

Problem:

(define (problem already-solved)
  (:domain trivial)
  (:init (p))
  (:goal (p))
)