Salvage Scout sacrifice no artifact in graveyard

[Tilo]

Can I still sacrifice Salvage Scout if there is no artifacts in my graveyard?

[Kenji]

Nope. You can't activate abilities or cast spells that require a target(s) if there isn't any valid target for the ability/spell.

[Tilaki]

I thought we werent' supposed to target artifacts in the graveyard anyway?

[Kenji]

Tilaki, please read Salvage Scout's rules text again:

W, Sacrifice Salvage Scout: Return target artifact card from your graveyard to your hand.

You'll notice that its ability speciically targets an artifact card in your graveyard. Compare it with something like Into Thin Air, which can only be used on artifacts that are on the battlefield. Here's the portion of the Comprehensive Rules that explains this:

114.2. Only permanents are legal targets for spells and abilities, unless a spell or ability (a) specifies
that it can target an object in another zone or a player, (b) targets an object that can’t exist on the
battlefield, such as a spell or ability, or (c) targets a zone.

Salvage Scout specifies that it targets an object in another zone, and Into Thin Air does not.