replace empty fields

[mlauber71]

If you ever need to do things the other way round and assign missing values, @ipazin had an idea for that too:

Replace specific row values of a column with NULL values

Sometimes Rule Engine, Variables and Null values can be tricky. I have added an example where you could define your own replacement rules. Age gets replaced by NULL and gender by “NA”. Please note: there is no generic NULL in the Rule engine but ipazin came up with an clever solution (Create or replace column with NULL values) - create a column with just missing and use that you would always need a TRUE rule that covers everything else. If you do not have one you will create missing values yo…