Trying to get property of non-object di codeigniter 3

Ada yg bisa bantu ? saya ingin menampilkan tampilan ke halaman krs_list berupa nama_lengkap, nim, program studi, dan tahun akademik, tetapi tidak bisa mengambil datanya melalui controller.

Controller Krs

public function index()
	{
		$data['judul'] = 'KRS';
		$data['user'] = $this->db->get_where('user', ['id_user' => $this->session->userdata('id_user')])->row_array();
		$datat = [
				'nim' => set_value('nim'),
				'id_tahun_aka' => set_value('id_tahun_aka')
		];
		$data['tahunakaseme'] = $this->Krs_model->getTahunAka();

		$this->form_validation->set_rules('nim', 'NIM', 'required|trim', ['required' => 'NIM Wajib Di Isi!']);
		$this->form_validation->set_rules('id_tahun_aka', 'Id Tahun Akademik', 'required|trim', ['required' => 'Id Tahun Akademik Wajib Di Isi!']);
		if($this->form_validation->run() == FALSE) {
			$this->load->view('themeplates_admin/header', $data);
			$this->load->view('themeplates_admin/sidebar', $data);
			$this->load->view('admin/krs/index', $data);
			$this->load->view('themeplates_admin/footer');
		} else {
			$this->krs_aksi();


		}
	}

	public function krs_aksi()
	{
		$nim = htmlspecialchars($this->input->post('nim', true));
		$tahun_akad = htmlspecialchars($this->input->post('tahun_akad'));

		// jika nim tidak ada di table Mahasiswa
		if($this->Krs_model->getMhsId($nim) == null) {
			$this->session->set_flashdata('pesan', '<div class="alert alert-danger" role="alert"><i class="fa fa-info-circle"></i> Data Mahasiswa <strong> Tidak Terdaftar!.</strong></div>');
			redirect('admin/krs');
		}

		$data = [
			'nim' => $nim,
			'id_tahun_aka' => $tahun_akad,
			'nama_lengkap' => $this->Krs_model->getMhsId($nim)->nama_lengkap
		];

		$data = [
				'krs_data' => $this->bacaKrs($nim, $tahun_akad),
				'nim' => $nim,
				'id_tahun_aka' => $tahun_akad,
				'tahun_aka' => $this->Krs_model->getTahunAkaId($tahun_akad)->tahun_aka,
				'semester' => $this->Krs_model->getTahunAkaId($tahun_akad)->semester == 'Ganjil' ? 'Ganjil' : 'Genap',
				'nama_lengkap' => $this->Krs_model->getMhsId($nim)->nama_lengkap,
				'prodi' => $this->Krs_model->getMhsId($nim)->nama_prodi
		];
		// $data['krs'] = $this->Krs_model->joinMhsProdiTahunAka($nim, $id_tahun_aka);

		$this->load->view('themeplates_admin/header', $data);
		$this->load->view('themeplates_admin/sidebar', $data);
		$this->load->view('admin/krs/krs_list', $data);
		$this->load->view('themeplates_admin/footer');
	}

	public function bacaKrs($nim, $tahun_akad)
	{
		$this->db->select('krs.id_krs, krs.kode_matkul, matkul.nama_matkul, matkul.sks');
		$this->db->from('krs');
		$this->db->where('krs.nim', $nim);
		$this->db->where('krs.id_tahun_aka', $tahun_akad);
		$this->db->join('matkul', 'matkul.kode_matkul = krs.kode_matkul');
		return $this->db->get()->result();	}

Modelnya

public function getTahunAka()
	{
		return $query = $this->db->query("SELECT id_tahun_aka, semester, CONCAT(tahun_aka, '/') AS thn_semester FROM tahun_aka")->result();
	}

	public function getMhsId($nim)
	{
		$this->db->where('nim', $nim);
		return $this->db->get('mahasiswa')->row();
	}

	public function getTahunAkaId($tahun_akad)
	{
		$this->db->where('id_tahun_aka', $tahun_akad);
		return $this->db->get('tahun_aka')->row();
	}