Android: QML Torch doesn't switch on

public class MyActivity extends org.qtproject.qt5.android.bindings.QtActivity
{
  ...

  private Camera m_camera = null;
  private Camera.Parameters m_camera_parameters = null;
  private boolean m_torch_enabled = false;

  private boolean has_flash() {
    PackageManager package_manager = getPackageManager();
    return package_manager.hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
  }

  private void open_camera() {
    if (m_camera == null) {
      try {
	m_camera = Camera.open();
	m_camera_parameters = m_camera.getParameters();
      } catch (Exception e) {
	// Camera is not available (in use or does not exist)
      }
    }
  }

  private void release_camera() {
    if (m_camera != null) {
      m_camera.stopPreview();
      m_camera.release();
      m_camera = null;
    }
  }

  private void _set_torch_mode(boolean enabled) {
    if (m_torch_enabled != enabled) {
      if (m_camera != null) {
	String flash_mode = enabled ? Camera.Parameters.FLASH_MODE_TORCH : Camera.Parameters.FLASH_MODE_OFF;
	m_camera_parameters.setFlashMode(flash_mode);
	m_camera.setParameters(m_camera_parameters);
	if (enabled)
	  m_camera.startPreview();
	else
	  m_camera.stopPreview();
	m_torch_enabled = enabled;
      }
    }
  }

  private void enable_torch() {
    _set_torch_mode(true);
  }

  private void disable_torch() {
    _set_torch_mode(false);
  }

  public void set_torch_mode(boolean enabled) {
    if (m_torch_enabled != enabled) {
      if (enabled) {
	if (has_flash()) {
	  open_camera();
	  enable_torch();
	}
      } else {
	disable_torch();
	release_camera();
      }
    }
  }

  <uses-permission android:name="android.permission.CAMERA" />
  <uses-permission android:name="android.permission.FLASHLIGHT"/>
  <uses-feature android:name="android.hardware.camera" android:required="false"/>