IF NOT NULL then UPDATE else keep the value of the field I think I am somehow close to get it work, but for some reason I still get errors.

I have the following UPDATE query:

UPDATE DeviceAttribute
SET Details = CASE Name
          WHEN 'Accessories' THEN @Accessories
          WHEN 'Description' THEN @Description
          WHEN 'Specification' THEN @Specification
          ELSE Details
END
WHERE DeviceID = 10


The parameters are filled in by different users. The problem I face now is that even when you want to update a single field you still have to fill out with the old data the other parameters. Therefore I would like to set the option IF @parameter IS NULL THEN keep the value that is already stored in the DB. I tried to find some solution and something like the following query seems to be the solution but I can't get it to work:

UPDATE DeviceAttribute
SET Details = CASE Name
          WHEN 'Accessories' IS NOT NULL THEN @Accessories
          WHEN 'Description' IS NOT NULL THEN @Description
          WHEN 'Specification' IS NOT NULL THEN @Specification
          ELSE Details
END
WHERE DeviceID = 10


THE DB is stored in SQL Server 2008

Thanks in advance for the help. 

EDIT for clarifying:

The original table looks like this

DeviceID|Name         |Details   |
     10 |Accessories  |earplugs  |
     10 |Description  |protectors|
     10 |Specification|BeatsByDre|


For publishing reasons I made a query to turn the tables. So when the Select query is ran the return table looks like the following

DeviceID|Accessories|Description|Specification|
     10 |earplugs   |protectors |BeatsByDre   |


I created a UI to let system users update the different fields like Accessories, Description,Specification.
The Update works if I update all fields with the query shown in the top. However when I Leave a textbox empty, then I get an error that the @parameter is missing a value. So trying to find a solution to update only the field where is something written. So if @parameter IS NULL then keep the original value in the DB. 
I found another solution which is really close to what I want but can't get it to work.
Here is the other solution: 
https://stackoverflow.com/questions/9387839/mysql-if-not-null-then-display-1-else-display-0
I think this will solve the issue:

UPDATE DeviceAttribute
SET Details = CASE Name
          WHEN 'Accessories'   THEN COALESCE(@Accessories, Details)
          WHEN 'Description'   THEN COALESCE(@Description, Details)
          WHEN 'Specification' THEN COALESCE(@Specification, Details)
          ELSE Details
              END
WHERE DeviceID = 10 ;


or this (to avoid redundant updates):

UPDATE DeviceAttribute
SET Details = CASE Name
          WHEN 'Accessories'   THEN @Accessories
          WHEN 'Description'   THEN @Description
          WHEN 'Specification' THEN @Specification
          ELSE Details
              END
WHERE DeviceID = 10 
  AND ( Name = 'Accessories'   AND @Accessories IS NOT NULL
     OR Name = 'Description'   AND @Description IS NOT NULL
     OR Name = 'Specification' AND @Specification IS NOT NULL
      ) ;


or this, using a table value constructor:

UPDATE da
SET da.Details = upd.Details
FROM DeviceAttribute AS da
  JOIN
    ( VALUES
      ('Accessories'   , @Accessories),
      ('Description'   , @Description),
      ('Specification' , @Specification)
    ) AS upd (Name, Details)
    ON upd.Name = da.Name 
WHERE da.DeviceID = 10
  AND upd.Details IS NOT NULL ;