I have 7 parameters (3 multi select of string, 1 DateTime, 3 string values) in my SSRS 2008 report, and I have set all the parameters as null in the default value.
It's working fine in my preview window of Visual Studio 2008. But after deployment to my report server, the "NULL" checkbox for the parameter is not checked, causing the report not to get loaded at initially.
This is "by design":
When you first deploy reports, parameters are uploaded with all their settings.
Administrators of those reports are then allowed to tweak the way report parameters function in the report web manager: change whether they accept null values, defaults, etc.
If you redeploy reports later, nothing is changed to existing parameters (the system doesn't want to "overwerite" changes made by report admins).
Solutions: