diff --git a/test/functional/test_framework/test_node.py b/test/functional/test_framework/test_node.py
--- a/test/functional/test_framework/test_node.py
+++ b/test/functional/test_framework/test_node.py
@@ -710,6 +710,8 @@
 def arg_to_cli(arg):
     if isinstance(arg, bool):
         return str(arg).lower()
+    elif arg is None:
+        return 'null'
     elif isinstance(arg, dict) or isinstance(arg, list):
         return json.dumps(arg, default=EncodeDecimal)
     else:
@@ -791,11 +793,6 @@
 
     def importprivkey(self, privkey, label=None, rescan=None):
         wallet_info = self.getwalletinfo()
-        if self.is_cli:
-            if label is None:
-                label = 'null'
-            if rescan is None:
-                rescan = 'null'
         if 'descriptors' not in wallet_info or (
                 'descriptors' in wallet_info and not wallet_info['descriptors']):
             return self.__getattr__('importprivkey')(privkey, label, rescan)
@@ -812,9 +809,6 @@
     def addmultisigaddress(self, nrequired, keys,
                            label=None):
         wallet_info = self.getwalletinfo()
-        if self.is_cli:
-            if label is None:
-                label = 'null'
         if 'descriptors' not in wallet_info or (
                 'descriptors' in wallet_info and not wallet_info['descriptors']):
             return self.__getattr__('addmultisigaddress')(
@@ -832,11 +826,6 @@
 
     def importpubkey(self, pubkey, label=None, rescan=None):
         wallet_info = self.getwalletinfo()
-        if self.is_cli:
-            if label is None:
-                label = 'null'
-            if rescan is None:
-                rescan = 'null'
         if 'descriptors' not in wallet_info or (
                 'descriptors' in wallet_info and not wallet_info['descriptors']):
             return self.__getattr__('importpubkey')(pubkey, label, rescan)
@@ -852,13 +841,6 @@
 
     def importaddress(self, address, label=None, rescan=None, p2sh=None):
         wallet_info = self.getwalletinfo()
-        if self.is_cli:
-            if label is None:
-                label = 'null'
-            if rescan is None:
-                rescan = 'null'
-            if p2sh is None:
-                p2sh = 'null'
         if 'descriptors' not in wallet_info or (
                 'descriptors' in wallet_info and not wallet_info['descriptors']):
             return self.__getattr__('importaddress')(