For template:
{{ TheVariable|save }}

I get error:
PHP Fatal error: Uncaught exception 'Twig_Error_Syntax' with message 'The filter "safe" does not exist in "index.twig" at line 2' in /path/to/lib/Twig/Node/Expression/Filter.php:29
Stack trace:
#0 /path/to/lib/Twig/Compiler.php(81): Twig_Node_Expression_Filter->compile(Object(Twig_Compiler))
#1 /path/to/lib/Twig/Node/Expression/Filter.php(41): Twig_Compiler->subcompile(Object(Twig_Node_Expression_Filter))
#2 /path/to/lib/Twig/Node/Expression/Filter.php(32): Twig_Node_Expression_Filter->compileFilter(Object(Twig_Compiler), Object(Twig_Filter_Function))
#3 /path/to/lib/Twig/Compiler.php(81): Twig_Node_Expression_Filter->compile(Object(Twig_Compiler))
#4 /path/to/lib/Twig/Node/Print.php(36): Twig_Compiler->subcompile(Object(Twig_Node_Expression_Filter))
#5 /path/to/lib/Twig/Node.php(106): Twig_Node_Print->compile(Object(Twig_Compiler))
#6 /path/to/lib/Twig in /path/to/lib/Twig/Node/Expression/Filter.php on line 29