Tablix is tied to a dataset which sources data from sql db and xml source | dataset merge kind of operation

I have a tablix on ssrs report which is mapped to a SQL dataset in the report 

The tablix has 4 columns and out of which 3 columns are mapped to SQL dataset and 1 mapped to xml data 

Note I use the following expression for the 1 xml column =join(LookupSet(1,1,Fields!xml.Value, "Flag"),",") to show data

Now when I have no data in SQL dataset and I  preview the report the SSRS doesn't show the data even when there is data in XML .

Can I force the tablix to show data even when the sql dataset doesnt have value and xml has value?