fix #3790

lib/wallet.py

@@ -367,6 +367,7 @@ class Abstract_Wallet(PrintError):
     def add_unverified_tx(self, tx_hash, tx_height):
         if tx_height == 0 and tx_hash in self.verified_tx:
             self.verified_tx.pop(tx_hash)
+            if self.verifier:
                 self.verifier.merkle_roots.pop(tx_hash, None)
 
         # tx will be verified only if height > 0