Internal error when hitting endpoint

I'm trying to get a manually-configured Lambda up using this example. When I hit the gateway API endpoint, I get this error in the CloudWatch logs:

```
"TypeError: Cannot read property 'indexOf' of undefined",
" at Function.getFileName (webpack:///./node_modules/bindings/bindings.js?:178:16)",
" at bindings (webpack:///./node_modules/bindings/bindings.js?:82:48)",
" at Object.eval (webpack:///./node_modules/libpq/index.js?:1:147)",
" at eval (webpack:///./node_modules/libpq/index.js?:361:30)",
" at Object../node_modules/libpq/index.js (/var/task/index.js:3785:1)",
" at __webpack_require__ (/var/task/index.js:20:30)",
" at eval (webpack:///./node_modules/pg-native/index.js?:1:13)",
" at Object../node_modules/pg-native/index.js (/var/task/index.js:5848:1)",
" at __webpack_require__ (/var/task/index.js:20:30)",
" at eval (webpack:///./node_modules/pg/lib/native/client.js?:11:14)"
```

My postgraphileOptions.js are as follows:
```
exports.options = {
dynamicJson: true,
cors: true,
graphiql: false,
graphqlRoute: '/graphql',
externalUrlBase: `/${process.env.AWS_STAGE}`,

// If consuming JWT:
// jwtSecret: process.env.JWT_SECRET || String(Math.random()),
// If generating JWT:
//jwtPgTypeIdentifier: process.env.JWT_PG_TYPE_IDENTIFIER,

/* If you want to enable GraphiQL, you must use `externalUrlBase` so PostGraphile
* knows where to tell the browser to find the assets. Doing this is
* strongly discouraged, you should use an external GraphQL client instead.

graphiql: true,
enhanceGraphiql: true,
graphqlRoute: '/',
graphiqlRoute: '/graphiql',
*/
};
```
I'd appreciate any help anyone could give.