change default entry sector value from null

[jere8184]

closes #1730

[heinezen]

You should not assign 0 or any valid portal ID. If you need to have this value uninitialized at the start, use std::optional.

[jere8184]

You should not assign 0 or any valid portal ID. If you need to have this value uninitialized at the start, use std::optional.

There's not necessarily a need for it to be uninitialized. The algorithm works fine no matter the value it starts with, which is why there's also no reason for it to be initialized in the first place; any initial value you choose is meaningless.

[heinezen]

There's not necessarily a need for it to be uninitialized. The algorithm works fine no matter the value it starts with, which is why there's also no reason for it to be initialized in the first place; any initial value you choose is meaningless.

This may be the case now but if we change the code and a bug is introduced that reads from the initial value 0, it might be really hard to debug since 0 is a valid ID. With std::optional, we could check for correct behavior. Using std::optional is also a good signifier to communicate that the value should be uninitialized at the start which is essentially how the initial state of the A* search is supposed to work.

[heinezen]

Very good!