ISNULL optional Parameter in SSRS

Display by Default all values with NULL Option in SSRS

Step 1:

Create a report with  data source and parameter with Isnull parameter as shown below

Step 2:  Preview the report. Here we are getting only given value's output

Step 3:Now go to parameter properties and mark the check box as shown below 

Step 4: Go to default values and select Specify values--> add-->(Null)-->OK

Step 5: Click on preview. Now you can find all values by default. If you want individual data like ware condition, un check the box and enter the value

Step 6: Compare the Step 2 and Step 5 to find the variation