For the data I already estimate the NA. My data has 10 covariates such as Bmi, Gender, Age, type of diabetes. For every covariates, i divided them into groups. For example, bmi we have under weight, normal, overweight and obese. And gender we have male and female. I find the possible combinations for each covariates such as gender female, bmi normal and age young adult. So,to calculate the posterior i need to know the prior prob and the covariates prob, but some of my data which is for bmi underweight, the probability are 0 which makes the posterior for each class become same value which is 0. So i dont know which class should i take if the three classes are 0.