PL/SQL: Generic function for converting arbitrary cursor to clob (delimited text)

Thanks to a couple of posts (namely TO_CHAR of an Oracle PL/SQL TABLE type and SQL*Plus tips. #2) I was able to develop very convenient and what's more important generic function for converting arbitrary cursor to clob lines or say any result set to clob lines.
Such function will be very useful for unloading results of an arbitrary query to delimited flat files.

function cursor_to_flat( a_cur in sys_refcursor, a_delimiter in varchar2, a_line_break in varchar2 ) 
return ty_clob_tbl pipelined 
as
  v_prev_rn pls_integer := 0;
  v_clob clob;
begin
  FOR cur_val IN (
    SELECT t.rn
      , EXTRACTVALUE ( t2.COLUMN_VALUE, 'node()' ) VALUE
    FROM ( select rownum rn, column_value from TABLE ( XMLSEQUENCE ( a_cur ) ) ) t
      , TABLE (XMLSEQUENCE ( EXTRACT ( t.COLUMN_VALUE, '/ROW/node()' ) ) ) t2
    order by 1
  ) LOOP
    if ( 0 = v_prev_rn ) then
      v_clob := cur_val.value;
    else
      if ( v_prev_rn != cur_val.rn ) then
        v_clob := v_clob || a_line_break;
        pipe row ( v_clob );
        v_clob := cur_val.value;
      else
        v_clob := v_clob || a_delimiter || cur_val.value;
      end if;
    end if;
    v_prev_rn := cur_val.rn;
  END LOOP;
  pipe row ( v_clob );
end;

Unit test code:

select *
from table( 
  pk_utils.cursor_to_flat( 
    cursor( 
      select 1, 2, 3 from dual 
      union all 
      select 4, 5, 6 from dual 
    ) 
  ) 
);

NB! One problem with this approach is that if you have NULLs in your result set, then they will be completely skipped (not wrapped with delimiters). Now I'm trying to solve it.

Edit
The author of SQL*Plus tips. #2 was totally awesome pointing out how to handle NULLs. Resulting function takes query as clob, but one can easily rollout version with sys_refcursor, as dbms_xmlgen.newcontext will accept it.

function query_to_flat( a_query in clob, a_delimiter in varchar2, a_line_break in varchar2 ) 
return ty_clob_tbl pipelined 
as
  v_prev_rn pls_integer := 0;
  v_clob clob;
  v_cur sys_refcursor;
  v_xml clob;
  v_context dbms_xmlgen.ctxtype;
begin
  v_context := dbms_xmlgen.newcontext( a_query );
  dbms_xmlgen.setnullhandling( v_context, dbms_xmlgen.empty_tag );
  v_xml := dbms_xmlgen.getxml( v_context );
  dbms_xmlgen.closecontext( v_context );
  
  for cur_val in ( 
    select row_num
      , col_value
    from xmltable( --<<<ML
'(#ora:view_on_null empty #){
for $a at $i in /ROWSET/ROW 
  , $r in $a/*
    return element ROW{
      element ROW_NUM{$i}
      , element COL_VALUE{$r/text()}
    }
}'
--ML;
      passing xmltype(v_xml)
      columns
        row_num   int
        , col_value varchar2(100)
    )
  ) loop
    if ( 0 = v_prev_rn ) then
      v_clob := cur_val.col_value; 
    else
      if ( v_prev_rn != cur_val.row_num ) then
        v_clob := v_clob || a_line_break;
        pipe row ( v_clob );
        v_clob := cur_val.col_value;
      else
        v_clob := v_clob || a_delimiter || cur_val.col_value;
      end if;
    end if;
    v_prev_rn := cur_val.row_num;
  END LOOP;
  pipe row ( v_clob );
end;

NB!This solution is still has some drawbacks for large dataset as all data is placed into variable, consuming PGA.
I'll try to address this issue in the following post.
Edit
And here's the followup post!