Can’t use method return value in write context – php Error

Yup, just to share – as usual.
While working on one of my projects I run this error. Here is the snippet where the error occurs:

....
        $carPrice = $this->getCarPrice(); // this would return object of CarPrice
        if (empty($carPrice->getCarPriceId()))
        {.....

Where $carPrice is an object to be returned after passing an array of data ($new_price) to the controller.
And on the next line, I was trying to if priceId of the car is not empty.
The problem is caused on the second operand of the if statement (empty($carPrice->getCarPriceId()) –
Here is how I get fool around..

...
$car_price_id = $carPrice->getCarPriceId();
if (empty($car_price_id))
{
...

It happens that function empty() [and even isset() ] do expect a variable to be checked otherwise, parse error will happen.

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