if (existingType != null) {
boolean isInstanceObject = existingType.isInstanceType();
if (isInstanceObject || fnName.equals("Function")) {
FunctionType existingFn =
isInstanceObject ?
existingType.toObjectType().getConstructor() :
typeRegistry.getNativeFunctionType(FUNCTION_FUNCTION_TYPE);
if (existingFn.getSource() == null) {
existingFn.setSource(sourceNode);
}