wallet_db.get_transaction: tolerate if tx_hash is None

Traceback (most recent call last):
  File "...\electrum\electrum\gui\qt\main_window.py", line 1503, in do_pay
    self.do_pay_invoice(invoice)
  File "...\electrum\electrum\gui\qt\main_window.py", line 1516, in do_pay_invoice
    self.pay_onchain_dialog(self.get_coins(), outputs)
  File "...\electrum\electrum\gui\qt\main_window.py", line 1570, in pay_onchain_dialog
    self.preview_tx_dialog(make_tx=make_tx,
  File "...\electrum\electrum\gui\qt\main_window.py", line 1574, in preview_tx_dialog
    d = PreviewTxDialog(make_tx=make_tx, external_keypairs=external_keypairs,
  File "...\electrum\electrum\gui\qt\transaction_dialog.py", line 654, in __init__
    self.update()
  File "...\electrum\electrum\gui\qt\transaction_dialog.py", line 392, in update
    tx_details = self.wallet.get_tx_info(self.tx)
  File "...\electrum\electrum\wallet.py", line 486, in get_tx_info
    tx_we_already_have_in_db = self.db.get_transaction(tx_hash)
  File "...\electrum\electrum\json_db.py", line 44, in wrapper
    return func(self, *args, **kwargs)
  File "...\electrum\electrum\wallet_db.py", line 822, in get_transaction
    assert isinstance(tx_hash, str)
AssertionError

Traceback (most recent call last):
  File "...\electrum\electrum\gui\qt\confirm_tx_dialog.py", line 65, in timer_actions
    self.update()
  File "...\electrum\electrum\gui\qt\transaction_dialog.py", line 392, in update
    tx_details = self.wallet.get_tx_info(self.tx)
  File "...\electrum\electrum\wallet.py", line 486, in get_tx_info
    tx_we_already_have_in_db = self.db.get_transaction(tx_hash)
  File "...\electrum\electrum\json_db.py", line 44, in wrapper
    return func(self, *args, **kwargs)
  File "...\electrum\electrum\wallet_db.py", line 822, in get_transaction
    if tx_hash is None:
AssertionError

electrum/wallet_db.py

@@ -818,7 +818,9 @@ class WalletDB(JsonDB):
         return self.transactions.pop(tx_hash, None)
 
     @locked
-    def get_transaction(self, tx_hash: str) -> Optional[Transaction]:
+    def get_transaction(self, tx_hash: Optional[str]) -> Optional[Transaction]:
+        if tx_hash is None:
+            return None
         assert isinstance(tx_hash, str)
         return self.transactions.get(tx_hash)