When run a "text file output" from Pentaho-Spoon, but some values are not output

Question

I want to create a file that executes SQL results. So, I create a transformation that consists of 'Table input - Text File output'. But it isn't working. If I see the "Table input - Preview rows", all columns are clearly printed, even the null value as I want. But some columns in the created text file are filled with a null value if even one row in a column has a null value. I don't know why. Please comment to me.

-- Expected

open a created text file
---------------------------------------
COLUMN_NAME1       COLUMN_NAME2
'N'                Hello World1
                   Hello World2
                   Hello World3

-- Result

Table input - preview rows
---------------------------------------
COLUMN_NAME1       COLUMN_NAME2
'N'                Hello World1
                   Hello World2
               Hello World3

open a created text file
---------------------------------------
COLUMN_NAME1       COLUMN_NAME2
                   Hello World1
                   Hello World2
                   Hello World3