Issue: Custom placeholders returns an array instead of a string

When using a custom placeholder that has a script, the placeholder content gets replaced with an array, instead of a string.

Example:

```yaml
preview: 
- /social/c7a0190c-831b-4019-a44a-692af75f95b9.png
```

This should be:

```yaml
preview: /social/c7a0190c-831b-4019-a44a-692af75f95b9.png
```