The attached TRDX file is created with the Standalone Report Designer tool
that accompanies your Telerik Reporting Q1 2014 installation. The report contains a single parameter that allows Null values to be selected. Also to retrieve data we use a data source component wrapping a parameterized data retrieval method (the data retrieval method parameter is mapped to the report parameter e.g. as in the steps in the SqlDataSource Wizard
Please compare the settings to yours, and verify the report parameter is mapped correctly to the data retrieval method's parameter, and the Null value is interpreted correctly.
In order to investigate the issue further, please send us test data and your report definition code to check the settings. If you prefer to not post these details in the forum, feel free to open a support ticket and attach your files there.
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