Oracle lê arquivo do diretório com exceção

  -- Open temporary lob
  DBMS_LOB.OPEN(dest_loc, DBMS_LOB.LOB_READWRITE);

  begin
    -- Load binary file into temporary LOB
    DBMS_LOB.LOADFROMFILE(
        dest_lob => dest_loc
      , src_lob  => src_loc
      , amount   => DBMS_LOB.getLength(src_loc));

  exception 
    when dbms_lob.operation_failed
    then
      return empty_blob();
  end;
..rest of your code.