NullPointerException：尝试调用虚方法'int android.graphics.Bitmap.getWidth()'

public class CategoryAdapter extends BaseAdapter {
Context context;
ArrayList<ModelCategory> model;
LayoutInflater layoutInflater;

public CategoryAdapter(Activity activity, ArrayList<ModelCategory> model) {
    this.model = model;
    this.context = activity;
}

@Override
public int getCount() {
    return model.size();
}

@Override
public Object getItem(int position) {
    return null;
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    ViewHolder viewHolder = null;
    layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    if (convertView == null) {
        viewHolder = new ViewHolder();
        convertView = layoutInflater.inflate(R.layout.category_adapter, parent, false);
        viewHolder.imageView = (ImageView) convertView.findViewById(R.id.category_grid_image);
        viewHolder.textView = (TextView) convertView.findViewById(R.id.get_category_title);
        convertView.setTag(viewHolder);

    } else {
        viewHolder = (ViewHolder) convertView.getTag();
    }

    viewHolder.textView.setText(model.get(position).getCategoryName());
    if(position<=3){
        viewHolder.imageView.setImageBitmap(StringToBitMap(model.get(position).getCategoryImage()));
    }
    else {
        viewHolder.imageView.setImageBitmap(getBitmap(model.get(position).getCategoryImage()));
    }
    return convertView;
}

private class ViewHolder {
    public ImageView imageView;
    public TextView textView;
}

private Bitmap getBitmap(String path) {

    BitmapFactory.Options option = new BitmapFactory.Options();
    option.inSampleSize = 8;
    Bitmap bitmap = BitmapFactory.decodeFile(path, option);
    Matrix matrix = new Matrix();
    matrix.postRotate(getImageOrientation(path));
    Bitmap rotatedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
    Bitmap resized = Bitmap.createScaledBitmap(rotatedBitmap, 150, 150, true);
    return resized;
}


private static int getImageOrientation(String imagePath) {
    int rotate = 0;
    try {
        File imageFile = new File(imagePath);
        ExifInterface exif = new ExifInterface(
                imageFile.getAbsolutePath());
        int orientation = exif.getAttributeInt(
                ExifInterface.TAG_ORIENTATION,
                ExifInterface.ORIENTATION_NORMAL);

        switch (orientation) {
            case ExifInterface.ORIENTATION_ROTATE_270:
                rotate = 270;
                break;
            case ExifInterface.ORIENTATION_ROTATE_180:
                rotate = 180;
                break;
            case ExifInterface.ORIENTATION_ROTATE_90:
                rotate = 90;
                break;
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

    return rotate;
}


public Bitmap StringToBitMap(String encodedString){
    try {
        byte [] encodeByte=Base64.decode(encodedString, Base64.DEFAULT);
        Bitmap bitmap=BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length);
        return bitmap;
    } catch(Exception e) {
        e.getMessage();
        return null;
    }
}

}

我得到 error 如下

java.lang.NullPointerException：尝试在com.adapter.CategoryAdapter的com.adapter.CategoryAdapter.getBitmap（CategoryAdapter.java:92）上的空对象引用上调用虚拟方法'int android.graphics.Bitmap.getWidth（）' .getView（CategoryAdapter.java:75）在android.widget.AbsListView.obtainView（AbsListView.java:2896）的android.widget.GridView.makeAndAddView（GridView.java:1456）android.widget.GridView.makeRow（GridView . java：361）在android.widget.GridView.fillDown（GridView.java:302）的android.widget.GridView.fillFromTop（GridView.java:437）在android.widget.GridView.layoutChildren（GridView.java:1284）at android.widget.AbsListView.onLayout（AbsListView.java:2700）位于android.view.Viewout上的android.view.View.layout（View.java:16899），android.widget . .onLayout（RelativeLayout.java:1077）在android.view.Viewout上的android.view.View.layout（View.java:16899），android.widget.FrameLayout.layoutChildren（FrameLa）上的android.view.Viewout.layout（ViewGroup.java:5405） yout.java:579）在Android.view.joutout（ViewLayout.java:514）android.view.View.layout（View.java:16899）android.view.ViewGroup.layout（ViewGroup.java:5405）的android.widget.FrameLayout.onLayout（FrameLayout.java:514） ）在android.view.View.layout（ViewGroup.java:5405）的android.view.View.layout（View.java:16899）的android.support.v4.widget.DrawerLayout.onLayout（DrawerLayout.java:1043）在android.widget.LinearLayout.setChildFrame（LinearLayout.java:1702）的android.widget.LinearLayout.onoutVertical（LinearLayout.java:1556）android.view上的android.widget.LinearLayout.onLayout（LinearLayout.java:1465） . 在android.view.View.layout（视图）的android.view.View.Viewout.Loutout（ViewLayout.java：1077）的android.view.View.Viewout（View.java:16899）上的View.layout（View.java:16899） .java：16899）在Android.widget.FrameLayout.onLayout（FrameLayout.java:514）的android.widget.FrameLayout.layoutChildren（FrameLayout.java:579）的android.view.ViewGroup.layout（ViewGroup.java:5405）在androi的android.view.View.layout（View.java:16899）在Android.widget.LineoutLayout的android.widget.LinearLayout.setoutVertical（LinearLayout.java：1556）的android.widget.LinearLayout.setChildFrame（LinearLayout.java:1702）的d.view.ViewGroup.layout（ViewGroup.java:5405） .onLayout（LinearLayout.java:1465）位于android.view.Viewout上的android.view.View.layout（View.java:16899），android.widget.FrameLayout.layoutChildren（FrameLayout . java：579）在android.view.View.Loutout（FrameLayout.java:514）的android.view.View.layout（View.java:16899）android.view.ViewGroup.layout（ViewGroup.java:5405）at android.widget.LinearLayout.setChildFrame（LinearLayout.java:1702）位于android.view.View.View的android.widget.LinearLayout.onLayout（LinearLayout.java:1465）android.widget.LinearLayout.layoutVertical（LinearLayout.java:1556）在Android.widget.FrameLayout.onLayout（FrameLayout . ）的android.widget.FrameLayout.layoutChildren（FrameLayout.java:579）的android.view.ViewGroup.layout（ViewGroup.java:5405）处的.layout（View.java:16899） . java的：5 14）在android.view.View.layout（View.java:16899）处于android.view.ViewGroup.layout（ViewGroup.java:5405）

我怎么解决这个问题？