Oracle Return true if a certain blockname exists

/* 

** Built-in:  FIND_BLOCK
** Example:  Return true if a certain blockname exists
*/
FUNCTION Does_Block_Exist( bk_name VARCHAR2 )
RETURN BOOLEAN IS
  bk_id Block;
BEGIN
  /*
  ** Try to locate the block by name
  */
  bk_id := Find_Block( bk_name );
  /*
  ** Return the boolean result of whether we found it.
  ** Finding the block means that its bk_id will NOT be NULL
  */
  RETURN (NOT Id_Null(bk_id));
END;