<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_extensions(self, support=None):
 """Returns filtered list of extensions in this registry :param support: Return only extensions with this extension support string, or None to return all extensions. :return: list of Extension objects """

        return [x for x in self.extensions.values() if support
                and support in x.supported or not support]