Extract all Elements with the same shared parameter

Hello everyone!
I am new to dynamo so please be kind with me if I ask something that sounds obvious.
I have a shared parameter in my project that contains a unique ID for every element used in the project. But not all ID’s have been assigned yet. I want to create a list with dynamo in order to find out what elements already have an ID and which elements do not.

You can easily get the list by using GetParameterByName node.
Every elements which does not have the ID parameter will return Null.