[!!!][BUGFIX] Preserve initial value of AOP-introduced properties
This maintains the initial value of AOP-introduced properties,
if they are other than NULL, for example::
/* @Flow\Introduce("class(TYPO3\Flow\Security\Context)") * @var string
protected $something = 'initialValue';
This is breaking in the rare case when the former behaviour,
which is setting the initial value to NULL, is expected
and relied on.