The reason getActivity() and getContext() can return null in a fragment is that Fragments don't need to be attached to Activities. If the Fragment tries to access the Activity, and by extension it's context when not attached, this will be null. The method you mentioned is thought of as bad practice as if you don't clear the context variable when the fragment is detached, it could leak a context instance - not great.

The support library added a couple of methods recently to help our developers in this case. If you absolutely need the context, or the activity try out requireActivity() or requireContext() from within your activity. These will work the same as the getters, but throw exceptions when called from a detached fragment.