title: Avoid SecurityException because of "No active admin owned by"
body: <p>How to avoid this Exception</p>
  
  <pre><code>E/AndroidRuntime(26113): Caused by: java.lang.SecurityException: No active admin owned by uid XXXX for policy #3
  </code></pre>
  
  <p>when calling this:</p>
  
  <pre><code>public static void lockScreen(Context context) {
      Log.d(TAG, "lockScreen");
      ComponentName mDeviceAdminSample = null;
      DevicePolicyManager dpm = (DevicePolicyManager) context.getSystemService(Context.DEVICE_POLICY_SERVICE);
      Intent intent = new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
      intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, mDeviceAdminSample);
      dpm.lockNow();
  }
  </code></pre>