Why is the inner "default" block needed here?

[mconigliaro]

I ran into this issue while trying to disable outbound email scanning for authenticated users in rspamd. Without the inner default block, the symbols_enabled = [] line doesn't seem to do anything. Credit goes to "notkoos" on Freenode for figuring out this workaround.

authenticated {
    priority = high;
    authenticated = yes;
    apply {
        default {
            symbols_enabled = [];
        }
    }
}