Shouldn't be "v4navProperty"?

[bsmykowskiinf]

Extensions/src/Microsoft.OData.Extensions.Migration/Middleware/QueryNodeTranslator.cs

Line 200 in fba558a

ExceptionUtil.IfNullThrowException(v4Type, "Unable to locate v4 navigation property " + nodeIn.NavigationProperty.Name);

[sigseg1v]

While I haven't tested this thoroughly, I think there might be an additional issue in this function for processing SingleNavigationNode.

Extensions/src/Microsoft.OData.Extensions.Migration/Middleware/QueryNodeTranslator.cs

Line 196 in fba558a

IEdmStructuredType v4Type = v4model.GetV4Definition(nodeIn.TypeReference.Definition) as IEdmStructuredType;

should likely be v4model.GetV4Definition(nodeIn.NavigationProperty.DeclaringType).

I was getting an issue at the same spot as you, which appeared at first that it was failing to catch the null navigation property, but the root issue is actually that it tries to read the navigation property from the navigation property type itself instead of from the type that declares it.