HELP: SSIS 2012 - Execute SQL Task with resultset to populate user variables produces DBNull error

Question

I am experiencing an unexplainable behavior with the Execute SQL Task control in SSIS 2012. The following is a description of how to simulate
the issue I will attempt to describe:
1. Create a package and add two variables User::varTest1 and User::varTest2 both of String type with default value of "Select GetDate()"
for each, have shown this to not matter as the same behavior occurs when using a fixed string value or empty string value.
2. Add a new Execute SQL Task to the control flow.
3. Configure an OLE DB connection.
4. Set SQLSourceType = "Direct Input"
5. Set the ResultSet property of the task to "Single Row"
6. In the ResultSet tab add two results as follows: 
Result Name: returnvalue1, Variable Name: User::varTest1
Result Name: returnvalue2, Variable Name: User::varTest2
7. Set an expression for the SqlStatementSource property with a string value of "Select 'Test' returnvalue1, 'Testing' returnvalue2'"
The idea is that the source would be dynamically set in order to run a t-sql statement which would have dynamic values for database name
or object that would be created at runtime and then executed to set the user variable values from its resultset. Instead what occurs is that a DBNull error occurs.
I am not sure if anyone else has experienced this behavior performing similiar actions with the Execute SQL Task or not. Any help would be
appreciated. The exact message is as follows:
[Execute SQL Task] Error: An error occurred while assigning a value to variable "varRestoreScript": "The type of the value
(DBNull) being assigned to variable "User::varRestoreScript" differs from the current variable type (String). Variables may not change type during execution. Variable types are strict, except for variables of type Object.
User::varRestoreScript is the first return value. And even with the a dummy select the same result occurs. I have narrowed the issue down
to the T-SQL Statement structure itself. 
The following works just fine within the execute sql task control as long as no resultset is configured for return:
"Declare @dynamicSQL nvarchar(max)
Select @dynamicSQL = name 
From sys.databases 
Where name = 'master'
Select atest_var1=@dynamicSQL, atest_var2='static'"
I have tried various iterations of the script above with no success. However, if I use the following derivative of it the task completes
successfully and variables are set as expected.  This will not work for my scenario however as I need to dynamically build a string spanning multiple resultsets to build one of the variable values.
"Select atest_var1=name, atest_var2='static'
From sys.databases
Where name = 'master'
I have a sample package which can reproduce this issue using the above code.  You can get to that through the post on www.sqlservercentral.com/Forums/Topic1582670-364-1.aspx
Scott

Answer 1

Arthur,  the query when executed doesn't return a null value for the @dynamicSQL variable.  It returns "master" as a string value.  Even the following fails which implements that suggestion:
Declare @dynamicSQL as nvarchar(max)
Select @dynamicSQL = name
From master.sys.databases 
Where name = 'master' -- (or any other DB name)
I believe I have found the cause of the issue.  It is datatype and size related.  The above script will properly set the variables in the resultset as long as you don't use nvarchar(max) or varchar(max).  This makes the maximum data size for
a String variable 4000 characters whether unicode or non-unicode typed.