ConfigMap data keys with leading underscore get removed

[felixscheinost]

I need to populate a ConfigMap with a key that is starting with a underscore but the resulting ConfigMap doesn't contain the expected keys.

Example:

  kubernetes.resources.configMaps.foo.data._FOO = "_bar";

It seems this like is the culprit:

kubenix/modules/k8s.nix

Line 21 in e4d0365

then mapAttrs (_n: moduleToAttrs) (filterAttrs (n: v: v != null && !(hasPrefix "_" n)) value)

Do you know what the purpose of this filter is?

I tried going back the git history but I reached cbf84e2 (first commit).