Include section ignored if using default local format

I've got an include instruction in my .gitlab file which is written like this :

include:
  - ".gitlab/libs/envvars/gitlab.yml"

It seems that it is not recognized if there is no "local:" section before. If I wrote it like that, the template is properly recognized :

include:
  - local: ".gitlab/libs/envvars/gitlab.yml"

Is it possible to add a default "local" value on this kind of include format, or at least give a hint to the user ?