protected void validate() {
    Preconditions.checkState(
        (mMultiImageRequests == null) || (mImageRequest == null),
        "Cannot specify both ImageRequest and FirstAvailableImageRequests!");
    Preconditions.checkState(
        (mDataSourceSupplier == null)
            || (mMultiImageRequests == null
                && mImageRequest == null
                && mLowResImageRequest == null),
        "Cannot specify DataSourceSupplier with other ImageRequests! Use one or the other.");
  }
Validates the parameters before building a controller.
drawee/src/main/java/com/facebook/drawee/controller/AbstractDraweeControllerBuilder.java