def METHOD_NAME(self, key, value=None):
    if key in self.data:
        if value is not None and value.strip() != "":
            self.data[key].remove(value)
        else:
            self.data[key] = []
        if len(self.data[key]) == 0:
            del(self.data[key])
            if key in self.keys:
                self.keys.remove(key)
    self.changed = True