Fix deletion issue

src/nemu/iproute.py

@@ -555,8 +555,11 @@ def get_bridge(br):
     iface = get_if(br)
     brdata = _sysfs_read_br(iface.name)
     # ports = [ifdata[1][x].index for x in brdata["ports"]]
-    del brdata["ports"]
-    return bridge.upgrade(iface, **brdata)
+    if brdata is not None:
+        del brdata["ports"]
+        return bridge.upgrade(iface, **brdata)
+    else:
+        return None
 
 
 def create_bridge(br):
@@ -598,6 +601,8 @@ def set_bridge(br, recover=True):
                     raise
 
     orig_br = get_bridge(br)
+    if orig_br is None:
+        return
     diff = br - orig_br  # Only set what's needed
 
     cmds = []