diff --git a/radicale/xmlutils.py b/radicale/xmlutils.py
index a069a7f..81da0b0 100644
--- a/radicale/xmlutils.py
+++ b/radicale/xmlutils.py
@@ -52,8 +52,11 @@ def _et_indent(element, level=0):
             element.tail = i
         for sub_element in element:
             _et_indent(sub_element, level + 1)
+        # sub_element is always defined as len(element) > 0
+        # pylint: disable=W0631
         if not sub_element.tail or not sub_element.tail.strip():
             sub_element.tail = i
+        # pylint: enable=W0631
     else:
         if level and (not element.tail or not element.tail.strip()):
             element.tail = i