Warning: Illegal offset type in _bootstrap_is_simple_string()

I have the same issue.

I guess we have this error because we try to do some string work on an object, as you can see here :

$string is a FieldFilteredMarkup object.

A simple patch that for the $string variable to actually be a string is attached.

Just updating the docblock.

Instead of assuming that every string passed will be an FieldFilteredMarkup object, which is not the intent of the procedural function and thus changes the function signature, it should instead do a check inside the function at the very top. Something like:

// Check if string is an object.
$string_clone = is_object($string) ? $string->__toString() : $string;

Because objects are natively passed by reference, and to avoid replacing the entire object, the rest of the code following this line in the function should be changed to reference the new $string_clone variable (or whatever name you think is better).

Thanks for the feedbacks. You're right, we should not assume that we'll always have a string here.

He is an updated patch.