From ce5adbafe5ad74127e5143cb77c0cdf360ae18d9 Mon Sep 17 00:00:00 2001
From: Junzi Sun <j.sun-1@tudelft.nl>
Date: Mon, 18 Apr 2022 11:27:53 +0200
Subject: [PATCH] Update bds20.py

---
 pyModeS/decoder/bds/bds20.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pyModeS/decoder/bds/bds20.py b/pyModeS/decoder/bds/bds20.py
index 914544e..d5f4b2f 100644
--- a/pyModeS/decoder/bds/bds20.py
+++ b/pyModeS/decoder/bds/bds20.py
@@ -24,9 +24,11 @@ def is20(msg):
     if d[0:8] != "00100000":
         return False
 
-    cs = cs20(msg)
+    # allow empty callsign
+    if common.bin2int(d[8:56]) == 0
+        return True
 
-    if "#" in cs and common.bin2int(d[8:56])>0: #message with empty callsign can still be BDS2,0
+    if "#" in cs20(msg):
         return False
 
     return True