The renderer.GetSymbol(GeoElement) method returns wrong result with the unique value renderer with multiple fields, if a field contains a null value.

Solução Provisória

If an attribute has a <no value>, replace it with the “<Null>” text. Example:

if (feature.Attributes["NrofPeople"] == null)

{

  feature.Attributes["NrofPeople"] = "<Null>";

}

var symbol = renderer.GetSymbol(feature);

Etapas para Reproduzir