Maksud error dan warning pada console

Warning

jQuery.Deferred exception: Cannot read property 'getContext' of null TypeError: Cannot read property 'getContext' of null
    at HTMLDocument.<anonymous> (http://localhost/0admin/3/files/assets/pages/dashboard/custom-dashboard.js:1:92)
    at j (http://localhost/0admin/3/files/bower_components/jquery/js/jquery.min.js:2:29999)
    at k (http://localhost/0admin/3/files/bower_components/jquery/js/jquery.min.js:2:30313) undefined

Error

Uncaught TypeError: Cannot read property 'getContext' of null
    at HTMLDocument.<anonymous> (custom-dashboard.js:1)
    at j (jquery.min.js:2)
    at k (jquery.min.js:2)

maksud dari code diatas apa ya gan? maklum masih belajar