Fix a minor bug in RecordPubli.authors_as_list.

modules/invenio_tools/recordpubli.py

@@ -111,7 +111,7 @@ class RecordPubli(Record):
             authors.append(first_author)
 
         # sometime the first author is missing
-        if first_author != authors[0]:
+        if first_author and len(authors) > 0 and first_author != authors[0]:
             authors.insert(0, first_author)
 
         return authors