# File lib/librarian/config/source.rb, line 36
      def []=(key, value)
        key_permitted?(key) or raise Error, "key not permitted: #{key.inspect}"
        value_permitted?(key, value) or raise Error, "value for key #{key.inspect} not permitted: #{value.inspect}"

        load!
        if value.nil?
          data.delete(key)
        else
          data[key] = value
        end
        save(data)
      end