fixed return types

Author: ShauryaDusht

data_structures/binary_tree/avl_tree.py

@@ -201,7 +201,7 @@ def get_balance(node: MyNode | None) -> int:
     return get_height(node.get_left()) - get_height(node.get_right())
 
 
-def get_min_value_node(node: MyNode | None) -> MyNode | None:
+def get_min_value_node(node: MyNode) -> MyNode:
     if node is None:
         return None
     current_node = node
@@ -369,4 +369,4 @@ def _test() -> None:
     random.shuffle(lst)
     for i in lst:
         t.del_node(i)
-        print(str(t))
+        print(str(t))