A simple yii2 function doesn't work

Question

I have two functions, which has the same purpose, but I wrote it differently. The first one works fine, but the second one - doesn't work and I can't see the difference between them. Could someone explain me why the second one doesn't work properly?

1.  public function getClientPhone() { if (is_null($this->client_id)) { return ''; } $phone = Client::getStaticClientPhone($this->client_id); if (is_null($phone)) { return '' ; } return $phone; } 

2.  public function getClientPhone() { $phone = Client::getStaticClientPhone($this->client_id); if ($this->client_id || $phone === null) { return ''; } return $phone; } 

Answer 1

Change

if ($this->client_id || $phone === null) {
    return '';
}

To

if ($this->client_id === null || $phone === null) {
    return '';
}

Or

if (!$this->client_id || $phone === null) {
     return '';
}