code: def _null_ria(direction, mechanism, purview, repertoire=None, phi=0.0):
      
      # TODO Use properties here to infer mechanism and purview from
      # partition yet access them with .mechanism and .partition
      return RepertoireIrreducibilityAnalysis(
          direction=direction,
          mechanism=mechanism,
          purview=purview,
          partition=None,
          repertoire=repertoire,
          partitioned_repertoire=None,
          phi=phi
      )
docs: The irreducibility analysis for a reducible mechanism.