public int addFile(File file,Long fileSize){
  int fileId=getFileId(file);
  if (fileSize != null)   fileSizes.set(fileId,fileSize);
  return fileId;
}

public int addFile ( File file , Long fileSize ) { int fileId = getFileId ( file ) ; if ( fileSize != null ) fileSizes . set ( fileId , fileSize ) ; return fileId ; }
add a file , if not already present and explicitly set its size
