How to build multiselect prompt using promptmany for DMR and cubes

When building a report in Report Studio against a Cube or a DMR, if you modify the expression of a data item in 
a LIST or in a CROSSTAB to put macro like : 

#promp('pline', 'memberuniquename', '[RootMember]', '')# You will be able to be prompted to select a SINGLE value and submit it. But, if you wish to select multiple values and submit them all at once, you may create a prompt page, add a value prompt in the prompt page, set the 'Multi Select' property of the prompt to 'Yes' and modify the macro above to use promptmany() like the following : #prompmany('pline', 'memberuniquename', '[RootMember]', '')# 

But, this will fail with the following error message when you select more than one item and submit.

Modify the promptmany macro as follow :

#promptmany('pline', 'memberuniquename', '[RootMember]', 'set(', '', ')')#

That will add the MUNs of the items properly in the promptmany function.