Fix issue #3251

qutebrowser/config/config.py

@@ -170,6 +170,11 @@ class KeyConfig:
 
     def bind(self, key, command, *, mode, save_yaml=False):
         """Add a new binding from key to command."""
+        if command is not None and not command.strip():
+            raise configexc.KeybindingError(
+                "Can't add binding '{}' with empty command in {} "
+                'mode'.format(key, mode))
+
         key = self._prepare(key, mode)
         log.keyboard.vdebug("Adding binding {} -> {} in mode {}.".format(
             key, command, mode))

tests/unit/config/test_config.py

@@ -285,6 +285,12 @@ class TestKeyConfig:
         key_config_stub.unbind('a')
         assert key_config_stub.get_command('a', mode='normal') is None
 
+    def test_empty_command(self, key_config_stub):
+        """Try binding a key to an empty command."""
+        message = "Can't add binding 'x' with empty command in normal mode"
+        with pytest.raises(configexc.KeybindingError, match=message):
+            key_config_stub.bind('x', ' ', mode='normal')
+
 
 class TestConfig: