external tables with tab-delimited columns

when loading data via an external table from a file with tab-delimited fields Oracle interprets two subsequent tabs incorrectly as one.

The followin definition works fine as long as there is a value in every field.

CREATE TABLE ext_testtab
(firsttestfield CHAR(255),
scdtestfield CHAR(255),
thrdtestfield CHAR(255))
ORGANIZATION EXTERNAL (
TYPE oracle_loader DEFAULT DIRECTORY Test_Export_dir
ACCESS PARAMETERS
(RECORDS DELIMITED BY ''
skip 1
BADFILE bad_file_dir: 'Test.bad'
LOGFILE log_file_dir: 'Test.log'
NODISCARDFILE
FIELDS TERMINATED BY '\t' OPTIONALLY ENCLOSED BY '"'
MISSING FIELD VALUES ARE NULL
)
LOCATION (
Test_Export_dir:Testfile.txt'
)
)
REJECT LIMIT 0
NOPARALLEL