For your scenario, to make the interpolation variable as an optional field, I could use the interpolation function called ExecuteIfIsNotNull.
You can use the ExecuteIfIsNotNull interpolation function in the URL of the GET method.
For more information about the ^[ExecuteIfIsNotNull](https://community.denodo.com/docs/html/browse/latest/en/vdp/administration/creating_data_sources_and_base_views/jdbc_sources/jdbc_sources#using-the-whereexpression-variable) syntax in the WHEREEXPRESSION Variable in the Virtual DataPort Administration Guide.
Additionally, if you still need help and if you are a user with valid support access then you can create a support case in [Denodo Support Site](https://support.denodo.com/) so that our support team will assist you further.
Hope this helps!