acf-kamailio database support does not allow for null or default value
If you leave a field blank, acf-kamailio puts an empty string. This causes failures for non-string types. Also, some tables, like lcr_gw, need to use null, and empty string is not the same.
We could check the input fields for the keywords “null” and “default”. On the off chance that users actually want to use the string “null” or “default” as a field value, we should allow them to put the value in quotes. Not sure how to handle if they actually want “null” (null in quotes), but I doubt that’s a serious issue. And, I don’t want to add null and default checkboxes for each field.
Also need to display “null” for null fields when viewing entries.
(from redmine: issue id 758, created on 2011-10-07, closed on 2013-05-21)