Make blank? default to false for all tags to maintain backwards compatible

lib/liquid/tag.rb

@@ -31,7 +31,7 @@ module Liquid
     end
 
     def blank?
-      @blank || true
+      @blank || false
     end
 
     def parse_with_selected_parser(markup)

lib/liquid/tags/assign.rb

@@ -29,6 +29,9 @@ module Liquid
       ''
     end
 
+    def blank?
+      true
+    end
   end
 
   Template.register_tag('assign', Assign)