Fix handling of none_ok in List/Dict

We now always return None (and '' as string) when the user configured an empty
list or dict.

qutebrowser/config/configdata.yml

@@ -21,6 +21,7 @@ yank_ignored_url_parameters:
   type:
     name: List
     valtype: String
+    none_ok: true
   default:
     - ref
     - utm_source
@@ -1232,6 +1233,7 @@ hints.hide_unmatched_rapid_hints:
 
 searchengines:
   default:
+    # FIXME:conf what if the user deletes/renames DEFAULT?
     DEFAULT: https://duckduckgo.com/?q={}
   type:
     name: Dict
@@ -1249,6 +1251,7 @@ aliases:
       name: String
       forbidden: ' '
     valtype: Command
+    none_ok: true
   desc: Command aliases FIXME
 
 # colors

tests/unit/config/test_configtypes.py

@@ -573,7 +573,8 @@ class TestList:
         except configexc.ValidationError:
             pass
         else:
-            assert typ.to_str(converted) == text
+            expected = '' if not val else text
+            assert typ.to_str(converted) == expected
 
 
 class TestFlagList:
@@ -1407,7 +1408,8 @@ class TestDict:
         except configexc.ValidationError:
             pass
         else:
-            assert d.to_str(converted) == text
+            expected = '' if not val else text
+            assert d.to_str(converted) == expected
 
 
 def unrequired_class(**kwargs):