public Slime applyDefaults(Slime slime, InnerCNode def) {
        applyDefaultsRecursive(slime.get(), def);
        return slime;
    }
Applies default values of a given config definition to a slime payload.
TODO: Support giving correct type of default values

@author Ulf Lilleengen
config/src/main/java/com/yahoo/vespa/config/DefaultValueApplier.java