parameter properties in report manager - "Has Default"

ok I've designed a report template that uses cascading paramters based
on several sp's. The user selects a value for the first parameter and
that value is passed to the sp that populates the second parameter
list. The value selected for the second param is used to populate the
third param list etc...
I want the first parameter to be required and the other 3 to be
optional - the report should still run if they are not selected. RS
BOL told me to go into the Report manager, select "Properties"
then"Parameters" and then select the "Has Default" check box for the
three optional paramters. This in turn enables the "Null" checkbox, so
I checked that box so null will be the default value passed if these
parameters are not selected.
By all accounts this should allow the report to run with only the first
parameter selected, but when run from Report Manager it still keeps
prompting the user to enter values for the 3 other optional parameters.
Any ideas? help?Never mind! found a workaround...