`KeyValuePipe` currently accepts `null` values as well as `Map`s and a
few others. However, due to the way in which TS overloads work, a type
of `T|null` will not be accepted by `KeyValuePipe`'s signatures, even
though both `T` and `null` individually would be.
To make this work, each signature that accepts some type `T` has been
duplicated with a second one below it that accepts a `T|null` and
includes `null` in its return type.
Fixes#35743
PR Close#36093
Fixes all TypeScript failures caused by enabling the `--strict`
flag for test source files. We also want to enable the strict
options for tests as the strictness enforcement improves the
overall codehealth, unveiled common issues and additionally it
allows us to enable `strict` in the `tsconfig.json` that is picked
up by IDE's.
PR Close#30993
Joey Perrott
JoostK
Paul Gschwendtner
Ingo Bürk
Pawel Kozlowski
Fabian Wiles