Update filter_logs to add protection

modules/harvest_tools/base.py

@@ -48,9 +48,15 @@ def filter_logs(logs):
         list
 
     """
+    if len(logs) == 0:
+        return logs
+
     data = [{"oais": dct["oais"]} for dct in logs]
     df = pd.DataFrame(data)
 
+    if df.empty:
+        return logs
+
     # tag primary OAI as cds or ins
     df["first_oai"] = df.oais.str.extract(r"oai:(\w{3})", expand=True)