test: add `bad-txns-prevout-null` test to mempool_accept.py

test/functional/mempool_accept.py

@@ -13,6 +13,7 @@ from test_framework.messages import (
     BIP125_SEQUENCE_NUMBER,
     COIN,
     COutPoint,
+    CTxIn,
     CTxOut,
     MAX_BLOCK_BASE_SIZE,
     MAX_MONEY,
@@ -247,6 +248,14 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
             rawtxs=[tx.serialize().hex()],
         )
 
+        self.log.info('A non-coinbase transaction with coinbase-like outpoint')
+        tx = tx_from_hex(raw_tx_reference)
+        tx.vin.append(CTxIn(COutPoint(hash=0, n=0xffffffff)))
+        self.check_mempool_result(
+            result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': 'bad-txns-prevout-null'}],
+            rawtxs=[tx.serialize().hex()],
+        )
+
         self.log.info('A coinbase transaction')
         # Pick the input of the first tx we signed, so it has to be a coinbase tx
         raw_tx_coinbase_spent = node.getrawtransaction(txid=node.decoderawtransaction(hexstring=raw_tx_in_block)['vin'][0]['txid'])