Checkbox for Mailchimp Interest Group

Hi,

I have hit the same issue with the same error message as here:

https://forum.grabaperch.com/forum/09-14-2018-mailchimp-interest-group

When using checkboxes to select interests, if one is left empty then the form doesn't submit to Mailchimp and I get the error. When using them as hidden fields as per the docs all works fine. I have included my code, short diagnostics and the error message below.

If this is a bug, is there a workaround at all or should I hang fire for a fix?

Thanks

Mike

Code Snippet

<perch:input type="checkbox" value="90982503db" id="london" mailer="interests">
<perch:label for="london">London</perch:label>

Error

{"type":"https://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/","title":"Invalid Resource","status":400,"detail":"Invalid interest ID: '_empty_'.","instance":"e0e29e36-f446-4a0b-a11f-8b66f539c3ae"}

Diagnostics

    Perch Runway: 3.1.2, PHP: 7.2.1, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: b396954eeb2d1d9ed7902b8bae237b287f21ad9e $, with PDO
    Server OS: Darwin, apache2handler
    Installed apps: content (3.1.2), assets (3.1.2), categories (3.1.2), perch_blog (5.6.1), perch_forms (1.12), perch_mailchimp (3.1), perch_twitter (4.0)
    App runtimes: <?php $apps_list = array( 'perch_blog', 'perch_forms', 'perch_twitter', 'perch_mailchimp' );
    PERCH_LOGINPATH: /admin
    PERCH_PATH: /Users/user/Desktop/Mike/Tara/tara/admin
    PERCH_CORE: /Users/user/Desktop/Mike/Tara/tara/admin/core
    PERCH_RESFILEPATH: /Users/user/Desktop/Mike/Tara/tara/admin/resources
    Image manipulation: GD
    PHP limits: Max upload 64M, Max POST 64M, Memory: 128M, Total max file upload: 64M
    F1: 3b606135b33e6a102526838f4152a807
    Resource folder writeable: Yes
    HTTP_HOST: tara.loc
    DOCUMENT_ROOT: /Users/user/Desktop/Mike/Tara/tara
    REQUEST_URI: /admin/core/settings/diagnostics/
    SCRIPT_NAME: /admin/core/settings/diagnostics/index.php