NullPointerException: When creating a SQLite DB
<p>this is the log i receive from android studio.</p>

<p>08-07 07:54:57.379 10573-10573/com.sifdon.shipping E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.sifdon.shipping, PID: 10573
                                                                     java.lang.RuntimeException: Unable to resume activity {com.sifdon.shipping/com.sifdon.shipping.DisplayActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.sifdon.shipping.DbHelper.getWritableDatabase()' on a null object reference
                                                                         at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3192)
                                                                         at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3223)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471)
                                                                         at android.app.ActivityThread.access$1200(ActivityThread.java:152)
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1341)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:135)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5538)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at java.lang.reflect.Method.invoke(Method.java:372)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
                                                                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase com.sifdon.shipping.DbHelper.getWritableDatabase()' on a null object reference
                                                                         at com.sifdon.shipping.DisplayActivity.displayData(DisplayActivity.java:157)
                                                                         at com.sifdon.shipping.DisplayActivity.onResume(DisplayActivity.java:149)
                                                                         at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1249)
                                                                         at android.app.Activity.performResume(Activity.java:6102)
                                                                         at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3167)
                                                                         at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3223) 
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2471) 
                                                                         at android.app.ActivityThread.access$1200(ActivityThread.java:152) 
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1341) 
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                         at android.os.Looper.loop(Looper.java:135) 
                                                                         at android.app.ActivityThread.main(ActivityThread.java:5538) 
                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                         at java.lang.reflect.Method.invoke(Method.java:372) 
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960) 
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
08-07 07:54:57.719 10573-10573/com.sifdon.shipping I/Process: Sending signal. PID: 10573 SIG: 9</p>