[BUGFIX] Mitigate "Using null as an array offset is deprecated"

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.

src/DocBlock/StandardTagFactory.php

@@ -282,8 +282,8 @@ final class StandardTagFactory implements TagFactory
             }
 
             $parameterName = $parameter->getName();
-            if (isset($locator[$typeHint])) {
-                $arguments[$parameterName] = $locator[$typeHint];
+            if (isset($locator[$typeHint ?? ''])) {
+                $arguments[$parameterName] = $locator[$typeHint ?? ''];
                 continue;
             }