Replace 3 fields with null in the file

Hi,
I have a file with 104 columns delimited by comma.

I have to replace fields 4,5 and 19 with null values and after replacing the columns in the file , the file should be still comma delimited. I am new to shell scripting, Experts please help me out.

Thank you

awk 'BEGIN{OFS=FS=","}{$4=$5=$19=""}{print}' input.csv > output.csv