close #88. not a complete solution, it just makes the problem visible…

… to users with eyes.

bauble/db.py

@@ -488,6 +488,9 @@ def make_note_class(name, compute_serializable_fields, as_dict=None, retrieve=No
     def is_defined(self):
         return bool(self.user and self.category and self.note)
 
+    def is_empty(self):
+        return not self.user and not self.category and not self.note
+
     def retrieve_or_create(cls, session, keys,
                            create=True, update=True):
         """return database object corresponding to keys

bauble/editor.py

@@ -1766,7 +1766,9 @@ def set_content(self, text):
         self.widgets.note_textview.set_buffer(buff)
         utils.set_widget_value(self.widgets.note_textview,
                                text or '')
-        buff.connect('changed', self.on_note_buffer_changed)
+        if not text:
+            self.presenter.add_problem(self.presenter.PROBLEM_EMPTY, self.widgets.note_textview)
+        buff.connect('changed', self.on_note_buffer_changed, self.widgets.note_textview)
 
     def __init__(self, presenter, model=None):
         super(NoteBox, self).__init__()
@@ -1891,10 +1893,13 @@ def on_category_entry_changed(self, entry, *args):
             value = None
         self.set_model_attr('category', value)
 
-    def on_note_buffer_changed(self, buff, *args):
+    def on_note_buffer_changed(self, buff, widget, *args):
         value = utils.utf8(buff.props.text)
         if not value:  # if value == ''
             value = None
+            self.presenter.add_problem(self.presenter.PROBLEM_EMPTY, widget)
+        else:
+            self.presenter.remove_problem(self.presenter.PROBLEM_EMPTY, widget)
         self.set_model_attr('note', value)
 
     def update_label(self):