This space intentionally left green.
While the rules don't explicitly state that a player 'must' play a tile, I think the 'must' can be assumed from this rule:
the rules wrote:
PASSING IF NO POSSIBLE PLACEMENT
If there are no legal placements for any of the building tiles held by a player, and all other players agree, the turn passes to the next player. The player who passed may attempt building placements as usual on subsequent turns.
Since a player may only pass is all players agree he has no valid placement, the converse, that a player 'must' play a tile if he can, must be true