Using `DocBlockFactory->create()` with a phpdocblock
hanging a `@throws` tag followed by a exception class
name emits following PHP 8.5.0 deprecation:
```
Using null as an array offset is deprecated,
use an empty string instead
```
in `StandardTagFactory->getArgumentsForParametersFromWiring()`.
This change uses the null-coalsce operator to fallback to
an empty string for the value which should be used as an
array key instead of using `null` to mitigate the deprecation
notice with PHP8.5.0 and matches the behaviour in earlier
PHP versions without the deprecation message.
