Cryptic "this.splice is not a function"

[captDaylight]

I'm new to a project using graphql-inspector and getting the error this.splice is not a function. My colleague's setup is working, so any helping figuring this out will be very helpful. Both localhost:4000 and the remote api are running.

the command:

graphql-inspector diff https://<our-domain>/api/graphql http://localhost:4000/api/graphql

the full error:

error TypeError: this.splice is not a function
    at HeadersList.append (/node_modules/cross-undici-fetch/dist/patch-headers-list.js:44:16)
    at Headers.append (/node_modules/undici/lib/fetch/headers.js:239:31)
    at fill (/node_modules/undici/lib/fetch/headers.js:56:15)
    at new Request (/node_modules/undici/lib/fetch/request.js:422:9)
    at new Request (/node_modules/@whatwg-node/fetch/dist/create-node-ponyfill.js:183:13)
    at fetch (/node_modules/@whatwg-node/fetch/dist/create-node-ponyfill.js:201:24)
    at defaultAsyncFetch (/node_modules/@graphql-tools/url-loader/cjs/defaultAsyncFetch.js:6:30)
    at /node_modules/@graphql-tools/url-loader/cjs/index.js:212:36
    at new ValueOrPromise (/node_modules/value-or-promise/build/main/ValueOrPromise.js:14:21)
    at executor (/node_modules/@graphql-tools/url-loader/cjs/index.js:186:20)

thx!