serializer function
Implementation
String serializer(DocumentNode doc, String sourceExpr, TypeNode typeNode) {
assert(typeNode is! ListTypeNode);
var sourceType = doc.findType(typeNode);
if (sourceType is EnumTypeDefinitionNode) {
return sourceExpr;
} else if (sourceType != null) {
return "${sourceExpr}?.toJson()";
} else {
return sourceExpr;
}
}