Fix default kwargs

bayesflow/experimental/networks/coupling_flow/couplings/coupling.py

@@ -17,7 +17,7 @@ def __init__(
     ):
         super().__init__()
 
-        self.transform = find_transform(transform, **kwargs.pop("transform_settings"))
+        self.transform = find_transform(transform, **kwargs.pop("transform_settings", {}))
         self.half_dim = half_dim
         self.subnet = find_subnet(
             subnet=subnet_builder,