Add item to ListView from SQLite

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.mariano.prototipo, PID: 1677 java.lang.NullPointerException at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188) at com.example.mariano.prototipo.conectionDB.getcaidas(conectionDB.java:53) at com.example.mariano.prototipo.caidasActivity.nuevacaida(caidasActivity.java:37) at com.example.mariano.prototipo.caidasActivity.access$000(caidasActivity.java:14) at com.example.mariano.prototipo.caidasActivity$1.onClick(caidasActivity.java:30) at android.view.View.performClick(View.java:4438) at android.view.View$PerformClick.run(View.java:18422) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5001) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) at dalvik.system.NativeStart.main(Native Method)