Issue with Multivalue report parameters optional functionality

Question

I am using SSRS 2012 reporting services to develop my SSRS report. I came across that I cannot have multi-value parameters as optional. In a report I have 5 parameters and 3 parameters (Invoice Type, Markupcode, Accountnum has multivalue selection so user
can select mutltiple accountnum or codes to get data). There is no option you can choose Allow null value. I went through various forums but unable to get worked. So I created this question. I am not doing any complex functionality, its very common functionality.
In the past I have used various reporting tools and never came across this issue. so please help here. I appreciate all your kind help. thanks.
Regards
Nitin

Answer 1

Hi Nitin,
As per my understanding, it seems that you want to build a multi-value parameter including the NULL value. By default, when we configure the parameter with the two options: Allow null value and Allow multiple values, we will receive an error message. To
work around this issue, we can use the ISNULL function to change null values to blank values (''). For more details, please refer to the following steps:
1. Modify the dataset used to retrieve data for the tablix like below:
SELECT id, invoiceType, markupCode, AccountNum FROM table WHERE ISNULL(invoiceType, '') IN (@InvoiceType)
2. Modify the dataset used to retrieve values for @InvoiceType like below:
SELECT DISTINCT ISNULL(invoiceType, '') AS invoice, ISNULL(invoiceType, 'NULL') AS InvoiceDescription FROM table
3. Modify parameter @InvoiceType, check Allow blank values ('') and Allow multiple values check boxes. Change the available values: Value field: @Invoice, Label field: InvoiceDescription.
The following screenshot is for your reference:
If you have any more questions, please feel free to ask.
Thanks,
Wendy Fu