handle confusion between bool and str around CheckboxWidget

wcs/fields.py

@@ -473,7 +473,7 @@ class BoolField(WidgetField):
         if not edit:
             kwargs['disabled'] = 'disabled'
             value = get_request().get_field(self.field_key)
-            form.add_hidden(self.field_key, value = value)
+            form.add_hidden(self.field_key, value=str(value))
             if value:
                 self.field_key = 'f%sdisabled' % self.id
                 get_request().form[self.field_key] = 'yes'
@@ -487,6 +487,20 @@ class BoolField(WidgetField):
         else:
             return ''
 
+    def convert_value_from_str(self, value):
+        if value is None:
+            return None
+        if value in (True, 'True', _('Yes'), 'yes'):
+            return True
+        return False
+
+    def convert_value_to_str(self, value):
+        if value is True:
+            return 'True'
+        elif value is False:
+            return 'False'
+        return value
+
     def stats(self, values):
         no_records = len(values)
         r = TemplateIO(html = True)