regression: Upload image with existing name results in 500 error without feedback

Steps to reproduce

1. Open a document and edit the (rich) text.
2. Insert image, create new image and upload from the dialog
3. Pick the same image and upload again

Expected: Dialog shows message that it's not allowed to upload image with same name (even better: have option to rename, this would be an improvement) No error logged in the cms log

Actual: 500 error page shows, no feedback in the UI. Two errors in the cms log:

20.02.2020 10:41:03 [catalina-exec-23] ERROR [org.hippoecm.frontend.editor.plugins.linkpicker.GalleryUploadPanel.createGalleryItem():227] A node with name picard_tiger_team.jpg already exists in folder /content/gallery. Not allowed to create same-name siblings

19.02.2020 20:37:51 [catalina-exec-134] ERROR [org.apache.wicket.DefaultExceptionMapper.mapUnexpectedExceptions():170] Unexpected error occurred org.apache.wicket.WicketRuntimeException: An error occurred while detaching component: [RootPlugin [Component id = root, page = org.hippoecm.frontend.PluginPage, path = root, type = org.hippoecm.frontend.plugins.cms.root.RootPlugin, isVisible = true, isVersioned = false], children = [TabbedPanel [Component id = tabs]][Component id = pinger][UserMenu [Component id = userMenu]][Component id = activeLogout][AbstractView [Component id = view]]]