Svelte Preprocess Babel Sourcemap Failure

When using svelte preprocess with typescript & babel,
if sourceMap option is enabled inside tsconfig.json.
webpack throws:

  ERROR in ./src/index.svelte 
  Module build failed (from ./node_modules/svelte-loader/index.js): 
  Error: .inputSourceMap must be a boolean, object, or undefined

else, if soruceMap is disable everything works as intended.

the error seems to come from autoProcess.ts

const script = async ({ content, attributes, filename, }) => {
    const transformResult = await scriptTransformer({
        content,
        attributes,
        filename,
    });
    let { code, map, dependencies, diagnostics } = transformResult;
    if (transformers.babel) {
        const transformed = await exports.runTransformer('babel', getTransformerOptions('babel'), {
            content: code,
            map
            filename,
            attributes,
        });
        code = transformed.code;
        map = transformed.map;
        dependencies = utils_1.concat(dependencies, transformed.dependencies);
        diagnostics = utils_1.concat(diagnostics, transformed.diagnostics);
    }
    return { code, map, dependencies, diagnostics };
};

transformResult.map seems to be a json string, and babel wants an object.

the following fixes the problem but i dont know if source map works as intended.

const script = async ({ content, attributes, filename, }) => {
    const transformResult = await scriptTransformer({
        content,
        attributes,
        filename,
    });
    let { code, map, dependencies, diagnostics } = transformResult;
    if (transformers.babel) {
        const transformed = await exports.runTransformer('babel', getTransformerOptions('babel'), {
            content: code,
            map: typeof map == "string" ? JSON.parse(map) : map, //fix
            filename,
            attributes,
        });
        code = transformed.code;
        map = transformed.map;
        dependencies = utils_1.concat(dependencies, transformed.dependencies);
        diagnostics = utils_1.concat(diagnostics, transformed.diagnostics);
    }
    return { code, map, dependencies, diagnostics };
};