Can't add a quote if the performer does not have an assigned character in the cast list

I have tried to add a quote to episode S06E01 of Black Mirror, specifically to the character played by Salma Hayek. This actress appears in the list of performers, but has no character assigned to her. This seems to be the cause of the attached error. I have tried with other actors who do have a character assigned in the same dropdown, and it does not give this error.