In a custom content app, we are using MagnoliaRichTextField in the detail sub-app. When a user tries to open a previous version of a record and the text field was empty in this version of the record, an exception is thrown. From what I gather, the conflict is between these two statements:

https://git.magnolia-cms.com/projects/PLATFORM/repos/ui/browse/magnolia-ui-vaadin-common-widgets/src/main/java/info/magnolia/ui/vaadin/richtext/MagnoliaRichTextField.java#84

and the following line in com.vaadin.ui.AbstractField#setValue(T, boolean):

 if (!SharedUtil.equals(newFieldValue, getInternalValue())) {

            // Read only fields can not be changed
            if (isReadOnly()) {
                throw new Property.ReadOnlyException();
            }
...

The problem seems to be that the value is supposed to be set to null but the field is already initialized with "". Since these values are not the same, the ReadOnlyException is triggered.