framework/base/Component.php
public function __isset($name)
    {
        $getter = 'get' . $name;
        if (method_exists($this, $getter)) {
            return $this->$getter() !== null;
        }

        // behavior property
        $this->ensureBehaviors();
        foreach ($this->_behaviors as $behavior) {
            if ($behavior->canGetProperty($name)) {
                return $behavior->$name !== null;
            }
        }

        return false;
    }
public function __isset($name)
    {
        $getter = 'get' . $name;
        if (method_exists($this, $getter)) {
            return $this->$getter() !== null;
        }

        // behavior property
        $this->ensureBehaviors();
        foreach ($this->_behaviors as $behavior) {
            if ($behavior->canGetProperty($name)) {
                return $behavior->$name !== null;
            }
        }

        return false;
    }
Checks if a property is set, i.e. defined and not null.

This method will check in the following order and act accordingly:

- a property defined by a setter: return whether the property is set
- a property of a behavior: return whether the property is set
- return `false` for non existing properties

Do not call this method directly as it is a PHP magic method that
will be implicitly called when executing `isset($component->property)`.
@param string $name the property name or the event name
@return bool whether the named property is set
@see https://secure.php.net/manual/en/function.isset.php