`system_syncState` RPC returns highestBlock null

[shunsukew]

Is there an existing issue?

• I have searched the existing issues

Experiencing problems? Have you tried our Stack Exchange first?

• This is not a support question.

Description of bug

system_syncState RPC returns null for highestBlock.
Confirmed with several chains using Substrate.

(Posted here because I don't know whether it is expected or a bug, and no description I could find about this field in internet)

Steps to reproduce

Option 1

• Go to Substrate portal https://polkadot.js.org/apps/?rpc=wss%3A%2F%2Frpc.polkadot.io#/rpc
• Call system syncState()

Option 2

• launch node by oneselve
• expose rpc with --rpc-port flag
• curl -H "Content-Type: application/json" -d '{"id":1, "jsonrpc":"2.0", "method": "system_syncState", "params":[]}' http://localhost:9933

[bkchr]

This was fixed by: #11979