fhdl: fix += for empty fragment

diff --git a/migen/fhdl/structure.py b/migen/fhdl/structure.py
index d00de9edb3de17de34e022a65388b6e5112bb591..2580cf0a2121a59e81e794576b670b697d1128d2 100644 (file)
--- a/migen/fhdl/structure.py
+++ b/migen/fhdl/structure.py
@@ -194,7 +194,7 @@ class Instance:
                return id(self)
 
 class Fragment:
-       def __init__(self, comb=StatementList(), sync=StatementList(), instances=[], pads=set()):
+       def __init__(self, comb=[], sync=[], instances=[], pads=set()):
                self.comb = _sl(comb)
                self.sync = _sl(sync)
                self.instances = instances