Representation of null in json

[mdicss]

Hi
In many APIs, you can have null-values for some configuration options. I see no way to use a variable in yaml to set a real value or to set null for such a option in the json file. Is there a way to do this or can this be added?
One example are maintenance windows. I use a json to configure different types of maintenance windows by setting values in the yaml file. One option is:
"dayOfWeek": "{{.dayOfWeek}}",
I can set this to a day of the week using a variable in the yaml file, but for daily maintenance windows, ther sould be:
"dayOfWeek": null,

How can I do this? A preprocessor would help here, see #522

Regards
Matthias