Missing choose option in search field for radio type entries

If you create a Radio button field for your database entries, there is no option "choosedots" anymore. In the past this was the case before resolving the issue -MDL-56725-, which sets the html_writer::select parameter explicitely to null.

As a consequence of this, you might not be able to set a filter for the database items, without using one of the options of the radio field.

Example: Database uses a text field for name and a Radio field for gender (m/w). As there is no neutral option for gender, you cannot filter all the persons with name = Smith, despite they are men or women.

Maybe I missed the intention of the change, but we ran in trouble with existing database activity instances on our moodle site, so it might be worth to think about a change?

Possible solution: Replace null with choosedot array like the default parameter in html_writer::select() method.

Replication Steps:

1. Create a database activity with a radio field with two options and a text field
2. Create two or more entries with same text in text field and different values in radio field
3. Try to search for this name

Your are not able to search for all entries  with same name, when they have different values in radio field.