defaulting values to a list

lib/arel/nodes/update_statement.rb

@@ -6,7 +6,7 @@ module Arel
       def initialize
         @relation = nil
         @wheres   = []
-        @values   = nil
+        @values   = []
       end
     end
   end

lib/arel/visitors/to_sql.rb

@@ -17,7 +17,7 @@ module Arel
           "UPDATE #{visit o.relation}",
           ("SET #{o.values.map { |column,value|
               "#{quote_column_name(column.name)} = #{quote visit value}"
-            }.join ', '}" if o.values),
+            }.join ', '}" unless o.values.empty?),
           ("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?)
         ].compact.join ' '
       end