Not able to introspect empty supergraph API

### Component

### What is the current behaviour?


### What is the expected behaviour?

There should be no errors.

### How to reproduce the issue?

Followed the steps [here](https://hasura.io/docs/3.0/getting-started/build/init-supergraph) and doing the step 4 fails with the following error:

```json
{
"errors": [
{
"message": "Failed to fetch",
"stack": "TypeError: Failed to fetch\n at https://console.hasura.io/assets/vendor-BLBR2gr0.js:367:3975\n at schemaFetcher (https://console.hasura.io/assets/GraphiQLHeaders-togRCAWA.js:103:30695)\n at https://console.hasura.io/assets/GraphiQLHeaders-togRCAWA.js:19:810\n at fetchIntrospectionData (https://console.hasura.io/assets/GraphiQLHeaders-togRCAWA.js:71:4616)\n at https://console.hasura.io/assets/GraphiQLHeaders-togRCAWA.js:71:5063\n at https://console.hasura.io/assets/GraphiQLHeaders-togRCAWA.js:71:5242\n at a2 (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:24296)\n at qf (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:42451)\n at S5 (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:36652)\n at Du (https://console.hasura.io/assets/vendor-BLBR2gr0.js:38:3288)\n at Lle (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:41328)\n at ac (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:40312)\n at GU (https://console.hasura.io/assets/vendor-BLBR2gr0.js:40:35759)\n at S (https://console.hasura.io/assets/vendor-BLBR2gr0.js:25:1535)\n at MessagePort.B (https://console.hasura.io/assets/vendor-BLBR2gr0.js:25:1894)"
}
]
}
```

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### Screenshots or Screencast

### Please provide any traces or logs that could help here.

### Any possible solutions/workarounds you're aware of?

### Keywords

Start by reproducing step 4 from the linked init-supergraph guide with an empty supergraph. Trace the Console's schemaFetcher and fetchIntrospectionData calls around the reported Failed to fetch error. Done means introspection completes without errors for the empty supergraph.

Written by the indexing model from the issue text.