Fix #29, commands smí nic nevrátit.

src/formatitko/transform_processor.py

@@ -477,7 +477,7 @@ class TransformProcessor:
 		if not self.context.get_command(e.attributes["c"]):
 			raise NameError(f"Command not defined '{e.attributes['c']}'.")
 		command_output = self.context.get_command(e.attributes["c"])(e, self.context)
-		e = e.replaceSelf(*command_output)
+		e = e.replaceSelf(*([] if command_output is None else command_output))
 		return self.transform(e)
 
 	def transform_InlineCommand(self, e: InlineCommand) -> Span: