@Nullable
  public Supplier<DataSource<IMAGE>> getDataSourceSupplier() {
    return mDataSourceSupplier;
  }
Gets the data source supplier if set.

<p>Important: this only returns the externally set data source (if any). Subclasses should use
{#code obtainDataSourceSupplier()} to obtain a data source to be passed to the controller.
drawee/src/main/java/com/facebook/drawee/controller/AbstractDraweeControllerBuilder.java