Fixing as_json to always use a simple Hash and remove nils. History updates.

lib/couchrest/model/properties.rb

@@ -12,6 +12,10 @@ module CouchRest
         raise "You can only mixin Properties in a class responding to [] and []=, if you tried to mixin CastedModel, make sure your class inherits from Hash or responds to the proper methods" unless (method_defined?(:[]) && method_defined?(:[]=))
       end
 
+      def as_json(options = nil)
+        Hash[self].reject{|k,v| v.nil?}.as_json(options)
+      end
+
       # Returns the Class properties
       #
       # ==== Returns