configtypes: Disallow ValidValues without values.

qutebrowser/config/configtypes.py

@@ -79,6 +79,8 @@ class ValidValues:
     """
 
     def __init__(self, *vals):
+        if not vals:
+            raise ValueError("ValidValues with no values makes no sense!")
         self.descriptions = {}
         self.values = []
         for v in vals:

tests/unit/config/test_configtypes.py

@@ -159,6 +159,10 @@ class TestValidValues:
     def test_repr(self, klass, args, expected):
         assert repr(klass(*args)) == expected
 
+    def test_empty(self, klass):
+        with pytest.raises(ValueError):
+            klass()
+
 
 class TestBaseType: