i will certainly try out the f-string. thank you @Tyler Retzlaff​ 

Options i tried:

1. With "None", it will not be able to concatenate with rest of the string. I get this error "can only concatenate str (not "NoneType") to str"
2. list(None) throws an error "Column is not iterable"
3. NULL - This will not work on spark, it will recognize it as an identifer.

Are there any other ways to specify blank?