diff --git i/test/functional/feature_block.py w/test/functional/feature_block.py
index 172af27848..8fad4ef4d3 100755
--- i/test/functional/feature_block.py
+++ w/test/functional/feature_block.py
@@ -1323,31 +1323,37 @@ class FullBlockTest(BitcoinTestFramework):
 
     def add_transactions_to_block(self, block, tx_list):
         [tx.rehash() for tx in tx_list]
         block.vtx.extend(tx_list)
 
     # this is a little handier to use than the version in blocktools.py
-    def create_tx(self, spend_tx, n, value, script=CScript([OP_TRUE, OP_DROP] * 15 + [OP_TRUE])):
+    def create_tx(self, spend_tx, n, value, script=None):
+        if script is None:
+            script = CScript([OP_TRUE, OP_DROP] * 15 + [OP_TRUE])
         return create_tx_with_script(spend_tx, n, amount=value, script_pub_key=script)
 
     # sign a transaction, using the key we know about
     # this signs input 0 in tx, which is assumed to be spending output 0 in spend_tx
     def sign_tx(self, tx, spend_tx):
         scriptPubKey = bytearray(spend_tx.vout[0].scriptPubKey)
         if (scriptPubKey[0] == OP_TRUE):  # an anyone-can-spend
             tx.vin[0].scriptSig = CScript()
             return
         sign_input_legacy(tx, 0, spend_tx.vout[0].scriptPubKey, self.coinbase_key)
 
-    def create_and_sign_transaction(self, spend_tx, value, script=CScript([OP_TRUE])):
+    def create_and_sign_transaction(self, spend_tx, value, script=None):
+        if script is None:
+            script = CScript([OP_TRUE])
         tx = self.create_tx(spend_tx, 0, value, script)
         self.sign_tx(tx, spend_tx)
         tx.rehash()
         return tx
 
-    def next_block(self, number, spend=None, additional_coinbase_value=0, script=CScript([OP_TRUE]), *, version=4):
+    def next_block(self, number, spend=None, additional_coinbase_value=0, script=None, *, version=4):
+        if script is None:
+            script = CScript([OP_TRUE])
         if self.tip is None:
             base_block_hash = self.genesis_hash
             block_time = int(time.time()) + 1
         else:
             base_block_hash = self.tip.sha256
             block_time = self.tip.nTime + 1
diff --git i/test/functional/test_framework/blocktools.py w/test/functional/test_framework/blocktools.py
index 338b7fa3b0..f2f01e7b7c 100644
--- i/test/functional/test_framework/blocktools.py
+++ w/test/functional/test_framework/blocktools.py
@@ -151,18 +151,20 @@ def create_coinbase(height, pubkey=None, *, script_pubkey=None, extra_output_scr
         coinbaseoutput2.nValue = 0
         coinbaseoutput2.scriptPubKey = extra_output_script
         coinbase.vout.append(coinbaseoutput2)
     coinbase.calc_sha256()
     return coinbase
 
-def create_tx_with_script(prevtx, n, script_sig=b"", *, amount, script_pub_key=CScript()):
+def create_tx_with_script(prevtx, n, script_sig=b"", *, amount, script_pub_key=None):
     """Return one-input, one-output transaction object
        spending the prevtx's n-th output with the given amount.
 
        Can optionally pass scriptPubKey and scriptSig, default is anyone-can-spend output.
     """
+    if script_pub_key is None:
+        script_pub_key = CScript()
     tx = CTransaction()
     assert n < len(prevtx.vout)
     tx.vin.append(CTxIn(COutPoint(prevtx.sha256, n), script_sig, SEQUENCE_FINAL))
     tx.vout.append(CTxOut(amount, script_pub_key))
     tx.calc_sha256()
     return tx
diff --git i/test/functional/test_framework/script.py w/test/functional/test_framework/script.py
index 97d62f957b..b8ecd48d4e 100644
--- i/test/functional/test_framework/script.py
+++ w/test/functional/test_framework/script.py
@@ -807,15 +807,17 @@ def BIP341_sha_scriptpubkeys(spent_utxos):
 def BIP341_sha_sequences(txTo):
     return sha256(b"".join(i.nSequence.to_bytes(4, "little") for i in txTo.vin))
 
 def BIP341_sha_outputs(txTo):
     return sha256(b"".join(o.serialize() for o in txTo.vout))
 
-def TaprootSignatureMsg(txTo, spent_utxos, hash_type, input_index = 0, scriptpath = False, script = CScript(), codeseparator_pos = -1, annex = None, leaf_ver = LEAF_VERSION_TAPSCRIPT):
+def TaprootSignatureMsg(txTo, spent_utxos, hash_type, input_index = 0, scriptpath = False, script = None, codeseparator_pos = -1, annex = None, leaf_ver = LEAF_VERSION_TAPSCRIPT):
     assert (len(txTo.vin) == len(spent_utxos))
     assert (input_index < len(txTo.vin))
+    if script is None:
+        script = CScript()
     out_type = SIGHASH_ALL if hash_type == 0 else hash_type & 3
     in_type = hash_type & SIGHASH_ANYONECANPAY
     spk = spent_utxos[input_index].scriptPubKey
     ss = bytes([0, hash_type]) # epoch, hash_type
     ss += txTo.version.to_bytes(4, "little")
     ss += txTo.nLockTime.to_bytes(4, "little")