How does Hidden Blade work when its target becomes invalid before resolution?

Ruling: If Hidden Blade's target becomes invalid before it resolves (e.g., removed from battlefield), the game cannot reference "its controller" and returns "null", so nothing is killed and no cards are drawn.

Sequence:

• Choose a valid target (a unit at a battlefield) when putting Hidden Blade on the chain
• The target cannot be changed once declared
• When Hidden Blade resolves, it checks if the target is still valid
• If the target is invalid, any checks for information about that target return "null"
• Both parts of the effect (kill and draw) resolve without effect

Nuances:

• If the target is moved back to base before resolution, both the kill and draw fail
• Playing Hidden Blade from hidden further restricts valid targets
• Zhonya's Hourglass does not prevent Hidden Blade from working because it replaces death with recall, but the target remains valid when Hidden Blade begins resolving, allowing the controller check to succeed
• Void Seeker differs from Hidden Blade because it doesn't perform further checks on its target after the kill attempt, so you still draw a card even if the target becomes invalid
• The target only needs to be valid when the spell begins to resolve, not throughout the entire resolution