What is the total number of unique values present in the 'stalk-root' feature, including the missing value…

What is the total number of unique values present in the 'stalk-root' feature, including the missing value…: a task in SmolDataEnvs-harbor-train-sandbox: 📊 SmolDataEnvs: Harbor (train) (Harbor dataset). Files (in /home/user/input, no subfolders): - mushrooms.csv