fixes warning

Author: huettenhain

refinery/units/sinks/ppxml.py

@@ -61,7 +61,7 @@ def indent(element: Element, level=0, more_sibs=False):
                 if more_sibs:
                     element.tail += pad
 
-        if root := dom.getroot():
+        if (root := dom.getroot()) is not None:
             indent(root)
 
         with io.BytesIO() as output: