Additional Info / Context :
I found this weakness, when trying to setup and subsequently render a field 'standalone', independent of any form.
In my case i needed a standaonone selectbox field on a page. Setting it up was no problem, but when attempting to render via $field->renderField(); , i stumbled over the issue described in this pull request.

Thanks for the pr. Can you add proper testing instructions? Like that people can test it and maintainers do understand where the issue is coming from.

Hi guys.
( Sorry i didn't have much time lately, work shedule is insane. )

So here is a very basic and simple example code, so you can test this for youself, easily, quickly and comfortably:

use Joomla\CMS\Form\Field\TextField;

$feld = new TextField();
$xmlstring = '
<field
		name="mytest"
		label="My Test Standalone Field"
		type="test" 
/> 
';
$xml = new SimpleXMLElement( $xmlstring );
$feld->setup( $xml );
$field =  $feld->renderField();

As you will see, the Application crashes, simply because of the afore mentioned inpropper check, that falsely and blindly assumes, that there is a contextual form assosiated with the field ( which is never the case, when you set up a 'standalone' field ) :

/libraries/src/Form/FormField.php line 1018+ :

        $options['inlineHelp'] = isset($this->form->getXml()->config->inlinehelp['button'])
            ? ((string) $this->form->getXml()->config->inlinehelp['button'] == 'show' ?: false)
            : false;

So you either implement this very simple and obvious fix, OR you decide completely to abandon any posibility to ever set up fields in this standalone manner via Joomla ever again, which would be a a complete waste, because standalone filelds are very useful and do profit from all the beautiful typical Joomla perks in regards to field's features, like e.g. skinnability ( layouts ), etc.

Again, the inaccuracy of the code here does not even have to to with Joomla per se, it's simply good coding practice to NEVER blindly assume anything at all, but to make sure. But of course, in this specific case, not fixing it would mean the completely unneccesary abandonment of a whole feature in Joomla!.
Do not abandon the ability to have standalone fields, please, for the love of Joomla!

Thanks for the pr. Can you add proper testing instructions? Like that people can test it and maintainers do understand where the issue is coming from.

Did now - I just updated the original post for the commit pull request.

Thanks, now we need some testers and then it can be merged.

Please update the priority; All Joomla! instances that use standalone fields are currently crashing on the respective pages.
Please do actually have a quick look at the code, and convience yorself by the mere fact of the nature of the change, that it is indeed, actually and literally a 1 minute fix and actually self-explanatory, even if you do not consider oder believe in the immense effects it has ( which is : Keeping the standalone fields feature alive of completely killing it, if this absolutely supersimple fix is not implemented ).

Even if you do not test it, the change is save and self-explanatory. Just have superquick look at the code, i',m begging you.

( I case i might sound impatient : I actually am, lol. It cannot be, that i have to update and fix the Joomla! core of several sites every time there's an update, just because of something brainlessly easily fixable like this. )

If possible, it would be nice to add a unit test. If we don't get any tests till the weekend. I'm going to merge this one as it indeed stabilizes the core code.

Thanks!!