Fix password passed to daemon.load_wallet

The password should not be an empty string.

Traceback (most recent call last):
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 377, in start_new_window
    wallet = self._start_wizard_to_select_or_create_wallet(path)
  File "/opt/electrum/electrum/gui/qt/__init__.py", line 446, in _start_wizard_to_select_or_create_wallet
    wallet = self.daemon.load_wallet(wallet_file, d['password'], upgrade=True)
  File "/opt/electrum/electrum/daemon.py", line 461, in func_wrapper
    return func(self, *args, **kwargs)
  File "/opt/electrum/electrum/daemon.py", line 474, in load_wallet
    wallet.unlock(password)
  File "/opt/electrum/electrum/wallet.py", line 3418, in unlock
    self.check_password(password)
  File "/opt/electrum/electrum/wallet.py", line 3069, in check_password
    raise InvalidPassword("password given but wallet has no password")
electrum.util.InvalidPassword: password given but wallet has no password

electrum/daemon.py

@@ -463,6 +463,7 @@ class Daemon(Logger):
 
     @with_wallet_lock
     def load_wallet(self, path, password, *, upgrade=False) -> Optional[Abstract_Wallet]:
+        assert password != ''
         path = standardize_path(path)
         wallet_key = self._wallet_key_from_path(path)
         # wizard will be launched if we return

electrum/gui/qt/__init__.py

@@ -442,8 +442,10 @@ class ElectrumGui(BaseElectrumGui, Logger):
         else:
             wallet_file = d['wallet_name']
 
+        password = d.get('password') or None  # convert '' to None
+
         try:
-            wallet = self.daemon.load_wallet(wallet_file, d['password'], upgrade=True)
+            wallet = self.daemon.load_wallet(wallet_file, password, upgrade=True)
             return wallet
         except WalletRequiresSplit as e:
             wizard.run_split(wallet_file, e._split_data)
@@ -454,8 +456,8 @@ class ElectrumGui(BaseElectrumGui, Logger):
             action = db.get_action()
             assert action[1] == 'accept_terms_of_use', 'only support for resuming trustedcoin split setup'
             k1 = load_keystore(db, 'x1')
-            if 'password' in d and d['password']:
-                xprv = k1.get_master_private_key(d['password'])
+            if password is not None:
+                xprv = k1.get_master_private_key(password)
             else:
                 xprv = db.get('x1')['xprv']
                 if not is_xprv(xprv):