fhdl/autofragment: empty build_fragment by default

diff --git a/migen/fhdl/autofragment.py b/migen/fhdl/autofragment.py
index 277ad76129daff93876b911b39a95574da208034..413b9d82fb2ad9eddaf21f69f5a8434bb58c18bb 100644 (file)
--- a/migen/fhdl/autofragment.py
+++ b/migen/fhdl/autofragment.py
@@ -120,4 +120,4 @@ class FModule:
                        object.__setattr__(self, name, value)
 
        def build_fragment(self):
-               raise NotImplementedError("FModule.build_fragment needs to be overloaded")
+               pass # do nothing (e.g. module has only submodules)