Enforce serialize_empty for repeated fields (#417)

tests/inputs/regression_414/test_regression_414.py

@@ -0,0 +1,15 @@
+from tests.output_betterproto.regression_414 import Test
+
+
+def test_full_cycle():
+    body = bytes([0, 1])
+    auth = bytes([2, 3])
+    sig = [b""]
+
+    obj = Test(body=body, auth=auth, signatures=sig)
+
+    decoded = Test().parse(bytes(obj))
+    assert decoded == obj
+    assert decoded.body == body
+    assert decoded.auth == auth
+    assert decoded.signatures == sig