Nigeria President Buhari won the election against Goodluck Jonathan in large part because of corruption and security concerns. In the 100 days since he took office, Buhari has been focused on fighting Boko Haram (including new leadership for the military) and corruption (including cleaning house in the state oil company). One of his anti-corruption moves was to delay appointing a cabinet until corruption reforms have been put in place.
But as this Reuters piece points out, having no cabinet carries costs. Nigeria has not developed a policy response to its economic challenges, including low oil revenues from the oil price crash.