ArrayList NullPointerException to ORMLite saving
===

I have an class Category 

  

      @DatabaseTable(tableName = "categories")
    public class Category {
    	public final static String CATEGORY_TITLE_FIELD_NAME  = "title";
    	@SerializedName("id")
    	@DatabaseField(id = true)
    	int id;
    	@SerializedName("title")
    	@DatabaseField(dataType = DataType.STRING, columnName = CATEGORY_TITLE_FIELD_NAME)
    	String title;
    	// need for ORMlite
    	public Category()
    	{}
    	public Category (int id, String title)
        {
            this.id = id;
            this.title = title;
        }
    	public int getCategoryId() 
    	{
    		
    		 return this.id;
        }
    		 
    	public String getCategoryTitle() 
    	{
    		 return this.title;
        }
    	
    	public void setCategoryId(int id)
    	{
    		 this.id = id;
    	}
    
    	public void setCategoryTitle(String title)
    	{
    		 this.title = title;
    	}
    	
    	@Override
    	public String toString()
    	{		
    	return "{title="+title +" "+"id="+id+"}";	
    	}
    	
    }

And I put data to it from JSON and want to save it in the ORMLite. This is how I do it:

    DatabaseHandler db = new DatabaseHandler(getApplicationContext());
    JSONObject data = json.getJSONObject(KEY_DATA);
    // getting categories
    JSONArray categories = new JSONArray();
    categories = data.getJSONArray(KEY_CATEGORIES);
    Gson gson = new Gson();
    JsonParser parser = new JsonParser();
    JsonArray array = parser.parse(categories.toString()).getAsJsonArray();
    Type listType = new TypeToken<List<Category>>() {}.getType();
    List<Category> tasks = new ArrayList<Category>();
    tasks = gson.fromJson(array.toString(), listType);
    RuntimeExceptionDao<Category, Integer> simpleDao = getHelper1().getSimpleCategoryDao();
    Dao<Category, Integer> categoryDao = getHelper1().getCategoryDao();
    saveContacts(tasks);
    List<Category> list = categoryDao.queryForAll();
    Log.i("categoryDAO",list.toString());

And this is saveContacts() method for data saving: 

     public void saveContacts(List<Category> contacts) throws SQLException
        {
        	OrmLiteSqliteOpenHelper dbHelper= DatabaseHandler.getInstance(_context);
            Dao<Category, Integer> daoContact=dbHelper.getDao(Category.class);
            for (Category contact : contacts) {
                daoContact.create(contact);
            }
            dbHelper.close();
        }

But I've got such exception as:

     FATAL EXCEPTION: main
    java.lang.NullPointerException
 	at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
 	at com.j256.ormlite.android.AndroidConnectionSource.getReadWriteConnection(AndroidConnectionSource.java:63)
    	at com.j256.ormlite.dao.BaseDaoImpl.create(BaseDaoImpl.java:304)
     	at com.assignmentexpert.LoginActivity.saveContacts(LoginActivity.java:192)
    	at com.assignmentexpert.LoginActivity$1.onClick(LoginActivity.java:108)
    	at android.view.View.performClick(View.java:2485)
     	at android.view.View$PerformClick.run(View.java:9080)
     	at android.os.Handler.handleCallback(Handler.java:587)
   	at android.os.Handler.dispatchMessage(Handler.java:92)
     	at android.os.Looper.loop(Looper.java:123)
    	at android.app.ActivityThread.main(ActivityThread.java:3687)
    	at java.lang.reflect.Method.invokeNative(Native Method)
     	at java.lang.reflect.Method.invoke(Method.java:507)
    	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
    	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
  	at dalvik.system.NativeStart.main(Native Method)

Please, tell what I'm doing wrong?

