<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _null_ria(direction, mechanism, purview, repertoire=None, phi=0.0):
 """The irreducibility analysis for a reducible mechanism."""

    # 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
    )