docs: @Nullable
  	private static EntropyInjectingFileSystem getEntropyFs(FileSystem fs) {
  		if (fs instanceof EntropyInjectingFileSystem) {
  			return (EntropyInjectingFileSystem) fs;
  		}
  		else if (fs instanceof SafetyNetWrapperFileSystem) {
  			FileSystem delegate = ((SafetyNetWrapperFileSystem) fs).getWrappedDelegate();
  			if (delegate instanceof EntropyInjectingFileSystem) {
  				return (EntropyInjectingFileSystem) delegate;
  			}
  			else {
  				return null;
  			}
  		}
  		else {
  			return null;
  		}
  	}