fix: instance variable @errors not initialized (#409)

lib/redis_client/cluster/errors.rb

@@ -43,11 +43,16 @@ def self.with_errors(errors)
         if !errors.is_a?(Hash) || errors.empty?
           new(errors.to_s).with_errors(EMPTY_HASH)
         else
-          messages = errors.map { |node_key, error| "#{node_key}: (#{error.class}) #{error.message}" }
+          messages = errors.map { |node_key, error| "#{node_key}: (#{error.class}) #{error.message}" }.freeze
           new(messages.join(', ')).with_errors(errors)
         end
       end
 
+      def initialize(error_message = nil)
+        @errors = nil
+        super
+      end
+
       def with_errors(errors)
         @errors = errors if @errors.nil?
         self
@@ -61,7 +66,7 @@ def self.from_command(command)
     end
 
     class NodeMightBeDown < Error
-      def initialize(_ = '')
+      def initialize(_error_message = nil)
         super(
           'The client is trying to fetch the latest cluster state ' \
           'because a subset of nodes might be down. ' \