The null entries in the layer definition of a utility network diagram template cause a SEVERE error(s) message "VariantType != VT_BSTR" returned in the feature service.

Workaround

1. Make a default version public.
2. Add electric UN from data owner database connection to active map in ArcGIS Pro.
3. Run the Create Diagram Layer Definition (Network Diagram) tool for each of the three diagrams with default selection settings. When the tool completes the layer definition field is populated in the Templates table.
4. Re-protect the default version.
5. Restarting feature service within Server Manager and SEVERE error is reproduced.

Steps to Reproduce