How To Ignor Filtering Criteria If There Is A Null Value For Parameter

I have gridview and i want to ignor that filtering if that parameter is empty how do i write that query.

my query is

select * from UserMAster where UserId=@USerID and RoleId=@RoleId

if @UserId is blank then i want to select all records without filtering with user Id a

nd if i have passed null or anything as parameter in roleId then alsoi want all the records if it contain value then i want to do filetring is it possible to with query. or else send me some alternative so that i don't need to execute more query.