Raihan. If no cards in my deck can I play a raihan. I still attach the energy from the discard pile but I don’t want to grab a card from the deck is this allowed. Can I fail grabbing a card from the deck if there are cards there and just attach the energy?
Raihan card text:
You can play this card only if any of your Pokemon were Knocked Out during your opponent's last turn.
Attach a basic Energy from your discard pile to 1 of your Pokemon. If you do, search your deck for a card and put it into your hand. Then, shuffle your deck.
You may play Raihan with no cards in deck, because the energy attach is the primary action. You may not play Raihan with no basic energy in discard.
However, you may not fail Raihan’s card search if you do have any cards in deck. The game doesn’t know what is in the deck, but it does know if you have any cards in it.
See for example the ruling on Computer Search, which has a similar unlimited search:
Can you use Computer Search and fail to find a card in your deck?
No, you cannot. When searching for a Pokemon, Trainer, or other particular type of card you can voluntarily fail the search because the contents of the deck are unknown; but when searching for "a card" of any kind the game can tell whether there are cards in the deck and you must take one if instructed to do so. Although the contents of the deck are unknown, the quantity of cards in the deck is known.