Search stored procedure


I have created a stored procedure for search.
This is the stored procedure code:

ALTER procedure [OS].[GET_ItemsRecords]
@itemID varchar (10) =  NULL,
@itemName varchar (100) =  NULL
select * from OS.Items where 
itemID  = @itemID  AND
itemName = @itemName;

I try to search using the itemID and it does not shows anything. The database only retrive the records when I enter in the item id and item name. How do i modify the search sql such that when I search for either the item id or item name, it displays the records. Also, if I enter the matching ID and Name, record will be displayed, else it will not be displayed. Thanks.