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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_scalars_plugin(self):
 """Tries to get the scalars plugin. Returns: The scalars plugin. Or None if it is not yet registered. """

    if scalars_metadata.PLUGIN_NAME in self._plugin_name_to_instance:
      # The plugin is registered.
      return self._plugin_name_to_instance[scalars_metadata.PLUGIN_NAME]
    # The plugin is not yet registered.
    return None