Row Permissions with not always existing session variable

[asinbo]

Is it strictly required to send all session variables, that are used in row permissions?
I am having problems with this:

• session variable might contain a list of features, the user has access to, but it doesn't have to!
  {"feature":{"name":{"_in":"x-hasura-allowed-features"}}} (my actual rule is a bit more complex with an _or, to check for other things as well)
• now, if the x-hasura-allowed-features isn't present, I get an error response saying "missing session variable: \"x-hasura-allowed-features\""

Is there any way to allow for missing session variables and check for null in the row permission setting?
I know, I could pass an empty list in my session variable; but I have some dynamically generated session variables as outcome of my authN webhook and the webhook doesn't know, what session variable could be expected (otherwise, I could add empty session variables).