fix #4255

gui/kivy/main_window.py

@@ -662,6 +662,8 @@ class ElectrumWindow(App):
 
     def get_max_amount(self):
         inputs = self.wallet.get_spendable_coins(None, self.electrum_config)
+        if not inputs:
+            return ''
         addr = str(self.send_screen.screen.address) or self.wallet.dummy_address()
         outputs = [(TYPE_ADDRESS, addr, '!')]
         tx = self.wallet.make_unsigned_transaction(inputs, outputs, self.electrum_config)