Formulator: option value should not be an empty string

2nd try

product/Formulator/Widget.py

@@ -1156,16 +1156,20 @@ class ListWidget(SingleItemsWidget):
       return "\n".join([list_widget, input_hidden])
 
     def render_item(self, text, value, key, css_class, extra_item):
-        if not text:
-            text = ' '
+        if text:
           return self.render_element('option', contents=text, value=value,
                                      extra=extra_item)
+        else:
+          return self.render_element('option', label=' ', value=value,
+                                     extra=extra_item)
 
     def render_selected_item(self, text, value, key, css_class, extra_item):
-        if not text:
-            text = ' '
+        if text:
           return self.render_element('option', contents=text, value=value,
                                      selected=None, extra=extra_item)
+        else:
+          return self.render_element('option', label=' ', value=value,
+                                     selected=None, extra=extra_item)
 
 ListWidgetInstance = ListWidget()
 
@@ -1199,16 +1203,20 @@ class MultiListWidget(MultiItemsWidget):
       return "\n".join([multi_list,input_hidden])
 
     def render_item(self, text, value, key, css_class, extra_item):
-        if not text:
-            text = ' '
+        if text:
           return self.render_element('option', contents=text, value=value,
                                      extra=extra_item)
+        else:
+          return self.render_element('option', label=' ', value=value,
+                                     extra=extra_item)
 
     def render_selected_item(self, text, value, key, css_class, extra_item):
-        if not text:
-            text = ' '
+        if text:
           return self.render_element('option', contents=text, value=value,
                                      selected=None, extra=extra_item)
+        else:
+          return self.render_element('option', label=' ', value=value,
+                                     selected=None, extra=extra_item)
 
 MultiListWidgetInstance = MultiListWidget()