Update to emit empty lists if asked for defaults

Author: danielgtaylor

betterproto/__init__.py

@@ -733,7 +733,7 @@ def to_dict(self, casing: Casing = Casing.CAMEL, include_default_values: bool =
                 elif isinstance(v, list):
                     # Convert each item.
                     v = [i.to_dict(casing, include_default_values) for i in v]
-                    if v:
+                    if v or include_default_values:
                         output[cased_name] = v
                 else:
                     if v._serialized_on_wire or include_default_values: