WIP: fix null value in lists (grpc)

src/main/java/org/caosdb/server/grpc/CaosDBToGrpcConverters.java

@@ -299,7 +299,7 @@ public class CaosDBToGrpcConverters {
   }
 
   private ScalarValue convertScalarValue(final IndexedSingleValue v) {
-    if (v == null) {
+    if (v == null || v.getWrapped() == null) {
       return ScalarValue.newBuilder()
           .setSpecialValue(SpecialValue.SPECIAL_VALUE_UNSPECIFIED)
           .build();