It has been detected that the flatten_dependencies_array() was fragile
and leading to wrong results when some incorrect data was passed to it.
This includes:
- Missing elements.
- Null dependencies.
- Non array dependencies.
While the existing behaviour (testing-wise) has been preserved, now the
situations above are better controlled and the function ignores all
those incorrect cases that shouldn't happen ever.
That implies that a good number of notices/warnings/errors aren't
happening anymore. That was impacting both results (when the problems
were only notices and warnings) and execution (when the problems
were errors).
Covered with tests.
e0d79c8e71