user defined function does not work in select statement

Hello,

I have a user defined function. But it does not work in select statement.

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drop function FN_TEST2;

create function FN_TEST2

(vInput nvarchar(100))

returns vReturn nvarchar(100)

LANGUAGE SQLSCRIPT

as

begin

    vReturn := 'Hello_' || vInput;

end;

--------------------

select FN_TEST2('abc123') as X from dummy;

----> It works. Output: Hello_abc123

--------------------

select FN_TEST2(BUKRS) as X from T001;

----> It doesn't work.

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Error message:

Could not execute 'select FN_TEST2(BUKRS) as X from T001' in 183 ms 883 µs .

SAP DBTech JDBC: [2048]: column store error: search table error: [6900] Attribute engine failed;L execution failed with rc=1697 ......

Where is my mistake???

BR

Y.Hu