How to load NCLOB from BFILE to Oracle DB

Question

I am trying to load some data from a file to NCLOB type in Oracle DB. File contains some multi-byte characters.

I followed this link and wrote a procedure to do that. But I see that some additional characters are being added to DB. Can anyone let me know what is wrong with the below code?

CREATE OR REPLACE PROCEDURE TEST_CLOB1_TGT_1537868348743 
 AS 
dest_TEXT3 NCLOB; 
src_TEXT3 BFILE := BFILENAME('EXAMPLE_LOB_DIR', 'TEXT3_TEST_CLOB1_TGT_1537868348743.lob'); 
dst_offset_TEXT3 number := 1 ;
src_offset_TEXT3 number := 1 ;
lang_ctx_TEXT3 number := DBMS_LOB.DEFAULT_LANG_CTX;
warning_TEXT3  number;

 BEGIN 

INSERT INTO "TEST_CLOB1_TGT" ("ID", "TEXT3") VALUES ( '1', EMPTY_CLOB() ) RETURNING TEXT3 INTO dest_TEXT3; 

DBMS_LOB.OPEN(src_TEXT3, DBMS_LOB.LOB_READONLY);
DBMS_LOB.LoadCLOBFromFile(
DEST_LOB => dest_TEXT3
,SRC_BFILE => src_TEXT3
,AMOUNT => DBMS_LOB.GETLENGTH(src_TEXT3) 
, DEST_OFFSET  => dst_offset_TEXT3 
, SRC_OFFSET  => src_offset_TEXT3 
, BFILE_CSID   => DBMS_LOB.DEFAULT_CSID 
, LANG_CONTEXT => lang_ctx_TEXT3 
, WARNING => warning_TEXT3 
); 
DBMS_LOB.CLOSE(src_TEXT3);

 COMMIT; 
 END; 
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