<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def MigrateInstance(r, instance, mode=None, cleanup=None):
 """ Migrates an instance. @type instance: string @param instance: Instance name @type mode: string @param mode: Migration mode @type cleanup: bool @param cleanup: Whether to clean up a previously failed migration """


    body = {}

    if mode is not None:
        body["mode"] = mode

    if cleanup is not None:
        body["cleanup"] = cleanup

    return r.request("put", "/2/instances/%s/migrate" % instance,
                     content=body)