private void addExtensions(SchemaDocument.Builder builder) {
        ObjectNode extensions = config.getSchemaDocumentExtensions();

        if (!extensions.isEmpty()) {
            LOGGER.fine(() -> "Adding JSON schema extensions: " + Node.prettyPrintJson(extensions));
            builder.extensions(extensions);
        }
    }
Perform the conversion of a single shape.

<p>The root shape of the created document is set to the given shape.
No schema extensions are added to the converted schema. This
conversion also doesn't take the shape predicate or private
controls into account.

@param shape Shape to convert.
@return Returns the created SchemaDocument.
smithy-jsonschema/src/main/java/software/amazon/smithy/jsonschema/JsonSchemaConverter.java