class cast exception when comparing double values

When a double value in a published document is edited, the field is empty when reviewing.

A stack trace is shown in the console:

Caused by: java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.String
at org.hippoecm.frontend.plugins.standards.diff.TextDiffModel.load(TextDiffModel.java:42)
at org.hippoecm.frontend.plugins.standards.diff.TextDiffModel.load(TextDiffModel.java:21)
at org.apache.wicket.model.LoadableDetachableModel.getObject(LoadableDetachableModel.java:120)
at org.apache.wicket.Component.getDefaultModelObject(Component.java:1720)
at org.apache.wicket.Component.getDefaultModelObjectAsString(Component.java:1739)
at org.apache.wicket.markup.html.basic.Label.onComponentTagBody(Label.java:114)
at org.apache.wicket.Component.renderComponent(Component.java:2686)