Silent invalid arguments -> None

gistfile1.diff

diff --git a/django/template/base.py b/django/template/base.py
index ab44bfb..3567756 100644
--- a/django/template/base.py
+++ b/django/template/base.py
@@ -551,9 +551,9 @@ class FilterExpression(object):
                 args = []
                 constant_arg, var_arg = match.group("constant_arg", "var_arg")
                 if constant_arg:
-                    args.append((False, Variable(constant_arg).resolve({})))
+                    args.append(mark_safe(Variable(constant_arg).resolve({})))
                 elif var_arg:
-                    args.append((True, Variable(var_arg)))
+                    args.append(Variable(var_arg))
                 filter_func = parser.find_filter(filter_name)
                 self.args_check(filter_name, filter_func, args)
                 filters.append((filter_func, args))
@@ -565,32 +565,34 @@ class FilterExpression(object):
         self.filters = filters
         self.var = var_obj
 
+    def resolve_var(self, var, context, ignore_failures=False):
+        if not isinstance(var, Variable):
+            return var
+        try:
+            return var.resolve(context)
+        except VariableDoesNotExist:
+            if ignore_failures:
+                return None
+            raise
+
     def resolve(self, context, ignore_failures=False):
-        if isinstance(self.var, Variable):
-            try:
-                obj = self.var.resolve(context)
-            except VariableDoesNotExist:
-                if ignore_failures:
-                    obj = None
-                else:
-                    if settings.TEMPLATE_STRING_IF_INVALID:
-                        global invalid_var_format_string
-                        if invalid_var_format_string is None:
-                            invalid_var_format_string = '%s' in settings.TEMPLATE_STRING_IF_INVALID
-                        if invalid_var_format_string:
-                            return settings.TEMPLATE_STRING_IF_INVALID % self.var
-                        return settings.TEMPLATE_STRING_IF_INVALID
-                    else:
-                        obj = settings.TEMPLATE_STRING_IF_INVALID
-        else:
-            obj = self.var
+        try:
+            obj = self.resolve_var(self.var, context, ignore_failures)
+        except VariableDoesNotExist:
+            if settings.TEMPLATE_STRING_IF_INVALID:
+                global invalid_var_format_string
+                if invalid_var_format_string is None:
+                    invalid_var_format_string = '%s' in settings.TEMPLATE_STRING_IF_INVALID
+                if invalid_var_format_string:
+                    return settings.TEMPLATE_STRING_IF_INVALID % self.var
+                return settings.TEMPLATE_STRING_IF_INVALID
+            else:
+                obj = settings.TEMPLATE_STRING_IF_INVALID
         for func, args in self.filters:
             arg_vals = []
-            for lookup, arg in args:
-                if not lookup:
-                    arg_vals.append(mark_safe(arg))
-                else:
-                    arg_vals.append(arg.resolve(context))
+            for arg in args:
+                arg_vals.append(self.resolve_var(arg, context,
+                    ignore_failures=True))
             if getattr(func, 'expects_localtime', False):
                 obj = template_localtime(obj, context.use_tz)
             if getattr(func, 'needs_autoescape', False):
@@ -853,6 +855,8 @@ def _render_value_in_context(value, context):
     means escaping, if required, and conversion to a unicode object. If value
     is a string, it is expected to have already been translated.
     """
+    if value is None:
+        return u''
     value = template_localtime(value, use_tz=context.use_tz)
     value = localize(value, use_l10n=context.use_l10n)
     value = force_unicode(value)