Oracle reports-Passing null parameters to RWRUN

I have a set of run-time parameters in the parameter form in oracle reports that have the "Restrict List to predetermined values". I am able to run the report in the report builder without supplying any value to these parameters. But during the batch run using RWRUN, I am getting the following warning and the report is not generated.

The value of restricted LOV parameter P_PARM1 is not among the selectable values

The above error occurs when I omit the parameter P_PARM1 altogether in the paramter list of RWRUN as well as when I supply it without giving any value to it(implying null) like below:

rwrun.sh <开发者_JAVA技巧other required parameters here> P_PARM1=

Any help would be much appreciated.

Does rwrun.sh ... P_PARM1='' yield anything different?