An error occurred while executing doInBackground()

Stack trace

java.lang.RuntimeException: An error occurred while executing doInBackground()
	at android.os.AsyncTask$3.done(AsyncTask.java:309)
	at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
	at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
	at java.util.concurrent.FutureTask.run(FutureTask.java:242)
	at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
	at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.bizo.momnkid.fragment.SubCategoryListFragment$CategoryAdapter.hideLoader(int, boolean)' on a null object reference
	at com.bizo.momnkid.fragment.SubCategoryListFragment$ImageDownloader.doInBackground(SubCategoryListFragment.java:277)
	at com.bizo.momnkid.fragment.SubCategoryListFragment$ImageDownloader.doInBackground(SubCategoryListFragment.java:243)
	at android.os.AsyncTask$2.call(AsyncTask.java:295)
	at java.util.concurrent.FutureTask.run(FutureTask.java:237)
	... 4 more