code: public void addCamera(@NonNull String cameraId, @NonNull CameraCharacteristics characteristics) {
      Preconditions.checkNotNull(cameraId);
      Preconditions.checkNotNull(characteristics);
      Preconditions.checkArgument(!cameraIdToCharacteristics.containsKey(cameraId));
  
      cameraIdToCharacteristics.put(cameraId, characteristics);
    }
docs: Adds the given cameraId and characteristics to this shadow.
  
  <p>The result from {@link #getCameraIdList()} will be in the order in which cameras were added.
  
  @throws IllegalArgumentException if there's already an existing camera with the given id.