Hi Rohith,
I had the same error in Dependent Modification, when I was doing GenIL for the first time, I solved it after 5 days of continuous debugging.
You need to Understand the Relation between Object ID and GUID, why object id is required when GUID itself is Unique, you can understand all this if you Understand GenIL well.
Now to solve you problem,
The Error is not in GET_KEY Method or in GET_OBJECT of your dependent,
This Error is because you are reading the Entity in a wrong way, while reading the entity In your case the GET_DYNAMIC_QUERY_DEFINITION you have a code to add objects to root list.
Here you are specifying the wrong key may be your key is made of two or more fields and there you are specifying just a single field.
Check it properly and you will get the Solution.
Thanks and Regards,
Pratheek