Compilation error: isset () cannot be used as a result of expression

Question

I get this error in the application that I am transferring from SF2.0.x to SF2.7:

[1] Symfony\Component\Debug\Exception\FatalErrorException: Compile Error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead) at n/a in /var/www/html/reptooln_admin/app/cache/dev/twig/68/7f/63589dd3687cb849dd68e6b6c10aa99eda1d82f95a5f3ac52a864d200499.php line 39 

I do not know what fails or how to fix it, so I need to advise. This is the line in the cache file where Stacktrace is reported:

  if ((((empty((isset($context["form_action"]) ? $context["form_action"] : $this->getContext($context, "form_action"))) == true) || (isnull((isset($context["form_action"]) ? $context["form_action"] : $this->getContext($context, "form_action"))) == true)) || (isset((isset($context["form_action"]) ? $context["form_action"] : $this->getContext($context, "form_action"))) == false))) { echo " "; $context["form_action"] = ""; echo " "; 

What I have TwigExtension:

 class PDOneTwigExtension extends \Twig_Extension { public function getFilters() { return array( 'var_dump' => new \Twig_Filter_Function('var_dump'), 'empty' => new \Twig_Filter_Function('empty', array($this, 'is_empty')), 'isset' => new \Twig_Filter_Function('isset', array($this, 'is_set')), 'isnull' => new \Twig_Filter_Function('isnull', array($this, 'is_null')), 'ucfirst' => new \Twig_Filter_Function('ucfirst', array($this, 'uc_first')), 'ucwords' => new \Twig_Filter_Function('ucwords', array($this, 'uc_words')), 'count' => new \Twig_Filter_Function('count', array($this, 'co_unt')), 'sizeof' => new \Twig_Filter_Function('sizeof', array($this, 'size_of')), 'concat' => new \Twig_Filter_Function('concat', array($this, 'concat')), 'in_array' => new \Twig_Filter_Function('in_array', array($this, 'inarray')), 'array' => new \Twig_Filter_Function('array', array($this, 'array_')), 'add_to_array' => new \Twig_Filter_Function('add_to_array', array($this, 'add_to_array')), 'replace' => new \Twig_Filter_Function('replace', array($this, 'replace')), 'htmlentitydecode' => new \Twig_Filter_Function('htmlentitydecode', array($this, 'htmlentitydecode')) ); } public function is_empty($sentence) { return empty($sentence) ? true : false; } // rest of methods goes here public function getName() { return 'pdone_twig_extension'; } } 

And I use the template as shown below:

 {% if form_action|empty == true or form_action|isnull == true or form_action|isset == false %} {% set form_action = '' %} {% endif %} 

Where could the problem be? Any tips?

Answer 1

From the documentation :

isset () only works with variables, because passing something else will result in a parsing error.

You do not pass the variable directly isset() . So you need to first compute the value, assign it to a variable, and then pass this to isset() .

For example, what you are doing at the moment is something like:

 if(isset($something === false)) { } // throws a parse error, because $something === false is not a variable 

Instead, you need to:

 $something = false; if(isset($something)) { ... } 

Answer 2

Why are you doing so much useless code?

Why not just:

 {% if form_action|empty == true %} {% set form_action = '' %} {% endif %}