Undefined array key "#other_option"

Hello efil,
Will you please add steps to reproduce the issue.

FWIW - this may be a backward compatibility issue. I used a prior version of this module w/o issue but the 4.1.0 version gave me the warning above. Looking at the code for my form I had
$form['QDR']['profile_qdr_institution_type']['#other'] = t('Other (please type a value)');.
Changing that to
$form['QDR']['profile_qdr_institution_type']['#other_option'] = t('Other (please type a value)');
resolved the warning.

Alternately, changing line 141 to use '#other' (not '#option' as proposed above) also resolved the issue.

This is about using the element in Form API.

Two things are kind-of distinct:

1) The issue text (though it's wrong), and comment #3: the fact that there used to be a '#other' value.

This is from D7 times. (AFAICT it silently disappeared during the rewrite, and it was then added back in ✨ How can we change the 'Other' field title or label Fixed .

People might still be trying to use it, because it was mentioned in the usage example → that is linked from the project page. I now edited the page to split it in a D8 and D7 example.

@qqmyers: AFAICT this means that in previous 4.x version, your "#other" was just ignored, and you got the default value ('-Other-') in 4.0.0.

2) The issue title: the PHP warning, which appeared in 4.1.0.

This (code assuming $element['#other_option'] is always set) was added by mistake in #3207231: "Other" option on taxonomy term field should only be available to users with permission → , because the issue only dealt with Field API fields and there are no automated tests that properly exercise Form API situations.

Patch attached. It's easy to fix because the static::addOtherOption() call has a default of '', so we just pass that.

Also adding something else to the patch: a default NULL for '#default_value' , so that the same PHP warning does not happen if you don't specify '#default_value' in the element definition. I don't see anything wrong with this.

(This needs a functional test that puts a minimal element definition on a form... to make sure no new warnings get introduced in the future. But without a test... at least the error gets fixed.)

Just tested the patch on a project and I can confirm that it worked fine and error was removed