piwigo: upload to HTTPS fails with certificate error, then crash

This is with Shotwell 0.30.4.

I recently switched my Piwigo site to use HTTPS, with a certificate from Let's Encrypt. When I try to log in to that site from Shotwell:

I get a certificate error, with two options:

If I click Show certificate, it brings up a blank new window with just a Close button. When I click Close, the application segfaults. In between, I see these messages on the console:

(.shotwell-wrapped:19454): GLib-GObject-CRITICAL **: 11:00:03.080: g_object_get: assertion 'G_IS_OBJECT (object)' failed
(.shotwell-wrapped:19454): Gcr-CRITICAL **: 11:00:03.080: gcr_simple_certificate_new: assertion 'data' failed
(.shotwell-wrapped:19454): GLib-CRITICAL **: 11:00:03.080: g_atomic_ref_count_dec: assertion 'g_atomic_int_get (arc) > 0'
 failed

I tried to see if I could back-trace in gdb, but I couldn't get it to show me anything. I assume that middle assertion failure is “down-stack” from PiwigoPublishing.vala:1040:

        info.clicked.connect (() => {
            var simple_cert = new Gcr.SimpleCertificate (cert.certificate.data);
            var widget = new Gcr.CertificateWidget (simple_cert);

but I'm not literate enough with this Glib/Vala ecosystem to trace why cert.certificate.data ends up being null.

If I click the other option, I understand, please proceed, it just goes back to the login window, with all fields except the password cleared out, and no messages on the console.

Thanks!