GraphQL-codegen fails to load GraphQLSchema - graphql

Question

So i have a problem loading a GraphQl schema using gql-codegen. When I try to generate, it fails with 404 error, however schema is available at http://localhost:8000/graphql below is the error.
Cannot convert undefined or null to object
TypeError: Cannot convert undefined or null to object
at Function.entries (<anonymous>)
I've tried to replace locahost with 127.0.0.1 in my npm file but i got the same result.
Any help is much appreciated. Thanks in advance!

Answer 1

After some debugging I found that the error comes from ../node_modules/#graphql-tools/url-loader/cjs/index.js from the following method:
class UrlLoader {
...
handleSDL(pointer, fetch, options) {
for (const [key, value] of Object.entries(options.headers)) {
if (key.startsWith(':')) {
// omit http2 headers
isHttp2 = true;
} else {
headers[key] = value
}
}
return new value_or_promise_1.ValueOrPromise(() => fetch(pointer, {
method: defaultMethod,
headers: typeof (options === null || options === void 0 ? void 0 : options.headers) === 'function' ? options.headers() : options === null || options === void 0 ? void 0 : options.headers,
}))
... }
The problem was that the options.headers property might be undefined or null, which cannot be iterated using Object.entries(). What solved my problem was adding a check to ensure that options.headers is defined before iterating through its entries:
if (options.headers) {
for (const [key, value] of Object.entries(options.headers)) {
// ...
}
}
And similarly, for the fetch call, I added a check to ensure that options.headers is defined before passing it to the fetch method.:
return new value_or_promise_1.ValueOrPromise(() => fetch(pointer, {
method: defaultMethod,
headers: typeof options?.headers === 'function' ? options.headers() : options?.headers || {},
}));
Then after running gql-gen again the error was gone and everything worked as expected.