SSIS variable of object type to string incorrect results

Hi, I am using SQL Server 2014 and for SSIS designer SSDT BI with Sisual studio 2013. I have the following query in an Execute SQL Task with Single resultset assigning the value to variable "role" of string data type.

SELECT DISTINCT (STUFF((SELECT CAST(',' + SubTableUser.UserRole AS VARCHAR(MAX))
		FROM TableUser AS SubTableUser
		WHERE SubTableUser.UserID = TableUser.UserID
		FOR XML PATH('')), 1, 1, '')) AS UserRole
FROM TableUser

Execute SQL Task Error:

The value type (__ComObject) can only be converted to variables of type Object.
An error occurred while assigning a value to variable "role": "The type of the value (DBNull) being assigned to variable 
"User::role" differs from the current variable type (String). Variables may not change type during execution. 
Variable types are strict, except for variables of type Object.".

I tried to assign the object variable value to a string variable in a script task

String.Format("{0}", Dts.Variables["User::role"])                                                                                   and get this value "System.__ComObject" instead of the actual value.

Thank you in advance.

SQLEnthusiast