avatar_url is null rather than "" in invite

[neilalexander]

Description

An incoming v2 invite event from Synapse seems to set avatar_url to nil rather than "", which doesn't match the spec's expectation of it being a string.

Steps to reproduce

• invite a user to a room
• observe request body, e.g.

{
  "event": {
    "auth_events": [
      "$uxl1r0IVu5dju5WaLyDWsiGkKu9VMpyLbTsXwVCSjg8",
      "$CDijC-qEh1F9wx2GaEDaVjZeZAotLyb9XECviqXYuQA",
      "$8u2LDvw2PQA1j7huGGlQ11_i1vYC_HLvPjyltQul1l0",
      "$r4MvBNTvC6aahOFhXUP2jHTAzLZDXYURLAipCNUD940",
      "$cmlp6_-XjUKXiKSsbnV0HSH9LXFw00r8Mu6eqG5RuWc"
    ],
    "content": {
      "avatar_url": "",
      "displayname": "neilalexander (Dendrite)",
      "membership": "invite"
    },
    "depth": 10,
    "hashes": {
      "sha256": "hl9idNvIrjXKVuUZwHdadEIsTk1hiul4Zqb5eJdrapk"
    },
    "origin": "synapse.neilalexander.dev",
    "origin_server_ts": 1587635800175,
    "prev_events": [
      "$8u2LDvw2PQA1j7huGGlQ11_i1vYC_HLvPjyltQul1l0"
    ],
    "prev_state": [
      
    ],
    "room_id": "!VRajJeEmcnrLJXqSoR:synapse.neilalexander.dev",
    "sender": "@neilalexander:synapse.neilalexander.dev",
    "signatures": {
      "synapse.neilalexander.dev": {
        "ed25519:a_MIwE": "B6IriXnW1afEYChG5/fSOl+nuUWDYg+IcITfx8vn0ZELyesuxxgDLjX0a5xVV0txd4cz9z829krkU95cSbUuBA"
      }
    },
    "state_key": "@neilalexander:dendrite.neilalexander.dev",
    "type": "m.room.member",
    "unsigned": {
      "age": 18,
      "invite_room_state": [
        {
          "content": {
            "join_rule": "invite"
          },
          "sender": "@neilalexander:synapse.neilalexander.dev",
          "state_key": "",
          "type": "m.room.join_rules"
        },
        {
          "content": {
            "name": "Test"
          },
          "sender": "@neilalexander:synapse.neilalexander.dev",
          "state_key": "",
          "type": "m.room.name"
        },
        {
          "content": {
            "avatar_url": null,
            "displayname": "neilalexander (Synapse)",
            "membership": "join"
          },
          "sender": "@neilalexander:synapse.neilalexander.dev",
          "state_key": "@neilalexander:synapse.neilalexander.dev",
          "type": "m.room.member"
        }
      ],
      "replaces_state": "$8u2LDvw2PQA1j7huGGlQ11_i1vYC_HLvPjyltQul1l0"
    }
  },
  "invite_room_state": [
    {
      "content": {
        "join_rule": "invite"
      },
      "sender": "@neilalexander:synapse.neilalexander.dev",
      "state_key": "",
      "type": "m.room.join_rules"
    },
    {
      "content": {
        "name": "Test"
      },
      "sender": "@neilalexander:synapse.neilalexander.dev",
      "state_key": "",
      "type": "m.room.name"
    },
    {
      "content": {
        "avatar_url": null,
        "displayname": "neilalexander (Synapse)",
        "membership": "join"
      },
      "sender": "@neilalexander:synapse.neilalexander.dev",
      "state_key": "@neilalexander:synapse.neilalexander.dev",
      "type": "m.room.member"
    }
  ],
  "room_version": "4"
}

Version information

• Homeserver: synapse.neilalexander.dev

If not matrix.org:

• Version: {"server_version": "1.11.0", "python_version": "3.7.6"}

• Install method: Docker matrixdotorg/synapse image ID d64d49dfd131

• Platform: Linux/VMware Photon OS 3.0 running Docker

[richvdh]

fixed by #7497