4 commits since v5.4.20

Changelog (excluding merges):
* (0d06996) [ghorsington] UnityInput: revert to null input in case of total failure
* (ea709e2) [ghorsington] Bump version
* (806d6d2) [ghorsington] UnityInput: remove hard dependency on Unity.InputManager (fixes #446)
* (a79d657) [ghorsington] UnityInput: Reformat, fix LegacyInputSystemAvailable not being static