Impossible filter empty values in table

[PaoloGuerra]

Hi,

have a table and I want to filter all null values in the field "Db_User_name". 
I deselected "Don't show null values" in all fields. But there is a lot a values empty in the table (yellow cells).

I checked the source data with notepad ++. It is a csv file. The corresponding field is empty.

There is an expression in the field "Db_user_name"

Spoiler

If(match(DB_User_Name_Comb_Machine_Learning,'NT AUTHORITY\SYSTEM', 'DBSNMP', 'SYS', 'UNISALUTE', 'APPS', 'WEB', 'SA', 'SYSTEM', 'EPVADMIN', 'SA', 'EDPSVIL', 'PRALFAUS', 'RPTVCF', 'APPLSYSPUB', 'CONSULTA', 'DW5', 'ZENA', '?')=0,
DB_User_Name_Comb_Machine_Learning,
Null()
)

I don't understand what the problem is

Can you help me please?

[PaoloGuerra]

Sorry, but I found the solution to the problem.

If(match(FieldName,'')=0,
FieldName,
Null()
)