Allow empty keys in config

TODO

@@ -40,7 +40,6 @@ Ctrl+A/X to increase/decrease last number in URL
 command completion gets hidden when doing a new ValueList value
 logging contexts
 catch import errors for PyQt and QtWebKit
-Allow binding to empty values for keys to override defaults
 How do we handle empty values in input bar?
 - Add more element-selection-detection code (with options?) based on:
       -> javascript: http://stackoverflow.com/a/2848120/2085149

qutebrowser/config/_conftypes.py

@@ -430,6 +430,8 @@ class Command(BaseType):
     typestr = 'command'
 
     def validate(self, value):
+        if not value:
+            return
         if value.split()[0] not in cmdutils.cmd_dict:
             raise ValidationError(value, "must be a valid command!")
 

qutebrowser/keyinput/_basekeyparser.py

@@ -309,7 +309,9 @@ class BaseKeyParser(QObject):
         if not sect.items():
             logging.warn("No keybindings defined!")
         for (key, cmd) in sect.items():
-            if key.startswith('<') and key.endswith('>'):
+            if not cmd:
+                continue
+            elif key.startswith('<') and key.endswith('>'):
                 keystr = self._normalize_keystr(key[1:-1])
                 logging.debug("registered special key: {} -> {}".format(keystr,
                                                                         cmd))