Type hinting cleanup

src/peakrdl_regblock/utils.py

@@ -1,5 +1,5 @@
 import re
-from typing import Match, Union
+from typing import Match, Union, Optional
 
 from systemrdl.rdltypes.references import PropertyReference
 from systemrdl.node import Node, AddrmapNode
@@ -45,6 +45,7 @@ def ref_is_internal(top_node: AddrmapNode, ref: Union[Node, PropertyReference])
 
     For the sake of this exporter, root signals are treated as internal.
     """
+    current_node: Optional[Node]
     if isinstance(ref, Node):
         current_node = ref
     elif isinstance(ref, PropertyReference):