For operands of the conditional operator, the data type DT_STR is only supported for input columns and cast operations. A ...

For operands of the conditional operator, the data type DT_STR is only supported for input columns and cast operations. A DT_STR operand that is not an input column or the result of a cast cannot be used with the conditional operation. To perform this operation, the operand needs to be explicitly cast with a cast operator.