I fixed the bug. Here is the solution:

modify org.outerj.xreporter.report.instance.Parameter

public void submit(Map submitValues, ExecutionContext executionContext, boolean rawLocale)
    {
        String value = (String)submitValues.get(getName());
        if (value != null && !value.equals(""))
        {
            enteredValue = value;
            ValidationResult validationResult = definition.getDataType().validate(value, executionContext, rawLocale);
            if (validationResult.isValid())
            {
                this.validationErrorMsg = null;
                this.value = validationResult.getValue();
            }
            else
            {
                this.validationErrorMsg = validationResult.getErrorMsg();
                this.value = null;
            }
        }
        else if (definition.isRequired())
        {
            this.value = null;
            enteredValue = "";
            validationErrorMsg =

executionContext.getResourceHandle().getBundle("org/outerj/xreporter/report/ReportMessages").getString("required-value");
        }

//XREPORTER XRP-8 BUG FIX
else if(!definition.isRequired() && (value==null || value.equals(""))){
this.validationErrorMsg = null;
this.value=null;
}
//END XRP-8 BUG FIX

Jasmeet,
(assuming it is proper for me to use that part of your name)

thx for your effort, it looks like we can actually
safely achieve the same by just adding:

else // !definition.isRequired() && (value == null || value.equals(""))
{
    this.validationErrorMsg = null;
    this.value=null;
}

i.e. we don't need to re-enforce the test actually...
-marc=

Added special junit testcase for this bug:
http://cvs.cocoondev.org/cgi-bin/viewcvs.cgi/xreporter/src/testcases/java/org/outerj/xreporter/http/test/PresidentListTest.java.diff?r1=1.2&r2=1.3&cvsroot=xreporter

And fixed it in cvs-head (will be in the next release)
http://cvs.cocoondev.org/cgi-bin/viewcvs.cgi/xreporter/src/java/org/outerj/xreporter/report/instance/Parameter.java.diff?r1=1.4&r2=1.5&cvsroot=xreporter

Thanks again Jasmeet!
-marc=

Administrative close (patch applied some time ago)