singleview: don't show line if field/widget renders empty string.

yaka/web/widgets.py

@@ -310,6 +310,15 @@ def render(self, model):
           continue
 
         value = Markup(field.render_view())
+        if value == u'':
+          # related models may have [] as value, but we don't discard this type
+          # of value in order to let widget a chance to render something useful
+          # like an 'add model' button.
+          #
+          # if it renders an empty string, there's really no point in rendering
+          # a line for this empty field
+          continue
+
         label = self.label_for(field, mapper, name)
         data[name] = (label,value,)