regtest: fix wallet load in Qt

docs/TESTING.md

@@ -60,3 +60,8 @@ a 20% chance of *each* yg bot rejecting the auth message and the tx message (bot
 20%). If you are running tumbler in adversarial conditions like that, consider
 changing things like the taker_utxo_retries or adding external commitments with
 the add-utxo tool so external commitments usage can be tested.
+
+### Testing Joinmarket-Qt with regtest
+
+You can follow the process above using `test/ygrunner.py` to set up the environment, and then just run `python joinmarket-qt.py` from within the `scripts` directory.
+Note that you can load a random/empty wallet with a 32 char hex string, or more usefully, use the provided wallet with coins in it, as described above. The 'generate' and 'recover' functions will not work on regtest for now, however; they can currently only be tested on mainnet.

scripts/joinmarket-qt.py

@@ -1382,7 +1382,7 @@ class JMMainWindow(QMainWindow):
             wallet_path = get_wallet_path(str(firstarg), None)
             try:
                 self.wallet = open_test_wallet_maybe(wallet_path, str(firstarg),
-                        None, ask_for_password=False, password=pwd.encode('utf-8'),
+                        None, ask_for_password=False, password=pwd.encode('utf-8') if pwd else None,
                         gap_limit=jm_single().config.getint("GUI", "gaplimit"))
             except Exception as e:
                 JMQtMessageBox(self,
@@ -1452,7 +1452,7 @@ class JMMainWindow(QMainWindow):
 
     def getTestnetSeed(self):
         text, ok = QInputDialog.getText(
-            self, 'Testnet seed', 'Enter a string as seed (can be anything):')
+            self, 'Testnet seed', 'Enter a 32 char hex string as seed:')
         if not ok or not text:
             JMQtMessageBox(self,
                            "No seed entered, aborting",