Seasonal adjustment with missing data

I have a monthly time-series of data from 1990-2018 but some months do not have any data and some months have mulitple data points.

Can I still use this method: https://www.mathworks.com/examples/econometrics/mw/econ-ex26256935-seasonal-adjustment-using-a-stable-seasonal-filter if I have missing data?

[KSSV]

HAve a look on fillmissing