Why my getDownloadUrl() has error ?

@Override
public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
mProgressBar.setProgress(0);
}
}, 500);

Toast.makeText(AddSolatPage.this, "Upload successful", Toast.LENGTH_LONG).show();
Upload upload = new Upload(solatTitle.getText().toString().trim(),
taskSnapshot.getDownloadUrl().toString());

}