Merge pull request #544 from seuros/master

change sql_state to attr_reader to avoid ruby warning

Author: sodabrew

lib/mysql2/error.rb

@@ -5,7 +5,8 @@ class Error < StandardError
     REPLACEMENT_CHAR = '?'
     ENCODE_OPTS      = {:undef => :replace, :invalid => :replace, :replace => REPLACEMENT_CHAR}
 
-    attr_accessor :error_number, :sql_state
+    attr_accessor :error_number
+    attr_reader   :sql_state
     attr_writer   :server_version
 
     # Mysql gem compatibility
@@ -18,10 +19,8 @@ def initialize(msg, server_version=nil)
       super(clean_message(msg))
     end
 
-    if "".respond_to? :encode
-      def sql_state=(state)
-        @sql_state = state.encode(ENCODE_OPTS)
-      end
+    def sql_state=(state)
+      @sql_state = ''.respond_to?(:encode) ? state.encode(ENCODE_OPTS) : state
     end
 
     private