Problem: I may forget to pass an optional param in cases where it should be...
Problem: I may forget to pass an optional param in cases where it should be provided.
Solution: Require the parameter, but also accept undefined.
This way, all call sites must explicitly specify all params.
This pattern is also useful temporarily, via this 3 step process:
1. Require the param initially. "Lean" on the compiler to see all the call sites that fail.
2. Audit all call sites to assure the param is being passed when it should be.
3. Make the param optional again.