flight/Engine.php
public function clear($key = null) {
        if (is_null($key)) {
            $this->vars = array();
        }
        else {
            unset($this->vars[$key]);
        }
    }
public function clear($key = null) {
        if (is_null($key)) {
            $this->vars = array();
        }
        else {
            unset($this->vars[$key]);
        }
    }
Unsets a variable. If no key is passed in, clear all variables.

@param string $key Key