@Override
    public Stream<ImmutableSDField> allImportedFields() {
        return importedFields
                .map(fields -> fields.fields().values().stream())
                .orElse(Stream.empty())
                .map(field -> field.asImmutableSDField());
    }
Returns an unmodifiable map of the onnx models available in this.
config-model/src/main/java/com/yahoo/schema/Schema.java