Paul is coming to the party tonight? I didn't know that!
What is the appropriate translation for "I didn't know that!" here?
Paul va venir à la fête ce soir ? Je ne le savais pas !
In particular, should the imparfait or the passé composé ("Je ne l'ai pas su !") be used? On the one hand, the knowledge is a state and not just one event, so we should use the imparfait. But the passé composé is quite often used for negative sentences similar to this.