admin: add unset command

sopel/modules/admin.py

@@ -339,6 +339,39 @@ def set_config(bot, trigger):
     setattr(section, option, value)
 
 
+@sopel.module.require_privmsg("This command only works as a private message.")
+@sopel.module.require_admin("This command requires admin privileges.")
+@sopel.module.commands('unset')
+@sopel.module.example('.unset core.owner')
+def unset_config(bot, trigger):
+    """Unset value of Sopel's config object.
+
+    Unsetting a value will reset it to the default specified in the config
+    defintion.
+
+    Trigger args:
+        arg1 - section and option, in the form "section.option"
+
+    If there is no section, section will default to "core".
+    """
+    # Get section and option from first argument.
+    parsed = parse_section_option_value(bot, trigger)
+    if parsed is False:
+        bot.reply('Usage: .unset section.option')
+        return
+
+    if not parsed:  # parsed = ()
+        # Bot already said "Option not found..."
+        return
+
+    (section, section_name, static_sec, option, value) = parsed
+    if value:
+        bot.reply('Invalid command; no value should be provided to unset.')
+        return
+
+    setattr(section, option, None)
+
+
 @sopel.module.require_privmsg
 @sopel.module.require_admin
 @sopel.module.commands('save')