# Objective
`Entity::PLACEHOLDER` acts as a magic number that will *probably* never
really exist, but it certainly could. And, `Entity` has a niche, so the
only reason to use `PLACEHOLDER` is as an alternative to `MaybeUninit`
that trades safety risks for logic risks.
As a result, bevy has generally advised against using `PLACEHOLDER`, but
we still use if for a lot internally. This pr starts removing internal
uses of it, starting from observers.
## Solution
Change all trigger target related types from `Entity` to
`Option<Entity>`
Small migration guide to come.
## Testing
CI
## Future Work
This turned a lot of code from
```rust
trigger.target()
```
to
```rust
trigger.target().unwrap()
```
The extra panic is no worse than before; it's just earlier than
panicking after passing the placeholder to something else.
But this is kinda annoying.
I would like to add a `TriggerMode` or something to `Event` that would
restrict what kinds of targets can be used for that event. Many events
like `Removed` etc, are always triggered with a target. We can make
those have a way to assume Some, etc. But I wanted to save that for a
future pr.
064e5e48b4