Here you assume that the ELSE always make reference to the "JError" object that you didn't tested.

To avoid any Fatal Error, I think that you need at least verify that the get() function exists and create a final else that put no code value.

So your code should become

if ($error instanceof Exception) {
    $code = $error->getCode();
} else if ( method_exists( $error, 'get')) {
    $code = $error->get('code');
} else {
    $code = '';
}

or if you prefer test the class type
if ($error instanceof Exception) {
    $code = $error->getCode();
} else if ($error instanceof Exception) {
    $code = $error->get('code');
} 
// In case this is another kind of Object with get function present (like derived of JObject)
else if ( method_exists( $error, 'get')) {
    $code = $error->get('code');
} else {
    $code = '';
}