Gtk3 crashes, icon "image-missing" not in theme Symbolic

[bootchk]

Context:
Ubuntu 19.04.
I am a developer running a Gimp plug-in (Python) in the Gimp app.
Opening a Gtk.FileChooserButton widget.
Expected widget to appear.
What happens: widget is garbled and console shows:

Gtk:ERROR:../../../../gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Icon 'image-missing' not present in theme Symbolic (gtk-icon-theme-error-quark, 0)

with a stack trace and opportunity to exit the plugin. Gimp continues to run (since plugin is separate process.)

See the issue filed against Gimp: https://gitlab.gnome.org/GNOME/gimp/-/issues/2029.
That report is on Gimp in Ubuntu 18.04. Still present with the latest Gimp (built myself) on Ubuntu19.04.

Installing the package gnome-icon-theme fixes the issue. As reported in Gimp #2029

It might be a packaging issue:
a missing dependency of the gtk3 package on package gnome-icon-theme.
Since package Gtk3 can crash unless gnome-icon-theme is also installed.

Probably it is a weakness of Gtk3, and would best be fixed there.
I.E. its a circularity issue: Gtk3 should not depend on an "image-missing" icon being in a theme to resolve the problem of an icon missing from the theme.
Or the Gtk3 developers have failed to convey a dependency to distributors like Ubuntu.

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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[bootchk (bootch)]

This is a packaging issue. The icon for "missing", which is in package gnome-icon-theme, MUST be installed with GTK.
The icon for "missing" is the fallback icon for GTK whenever it can't find an icon.
If GTK package does not depend on gnome-icon-theme, then GTK will crash when it needs the icon for "missing."