The EnumRepresentationConvention does not currently apply to nullable enums.

i.e. nullable enums are persisted using integer values even when the EnumRepresentationConvention is applied.

EnumRepresentationConvention should apply to nullable enums.

This is a slight backward breaking change in that the serialization format of nullable enums might change when using this convention. That won't be a problem for round tripping because the Deserialize method accepts either integers or strings, but must be taken into account if writing queries against the nullable enum field.