Merged from 7.43.1.dev0

Guard against reference sections without names. [from revision 19892]
 - Legacy-Id: 19894

Author: jennifer-richards

ietf/utils/xmldraft.py

@@ -69,11 +69,12 @@ def _document_name(self, anchor):
 
     def _reference_section_type(self, section_name):
         """Determine reference type from name of references section"""
-        section_name = section_name.lower()
-        if 'normative' in section_name:
-            return self.REF_TYPE_NORMATIVE
-        elif 'informative' in section_name:
-            return self.REF_TYPE_INFORMATIVE
+        if section_name:
+            section_name = section_name.lower()
+            if 'normative' in section_name:
+                return self.REF_TYPE_NORMATIVE
+            elif 'informative' in section_name:
+                return self.REF_TYPE_INFORMATIVE
         return self.REF_TYPE_UNKNOWN
 
     def get_refs(self):