Unity-Technologies/UnityCsReference · error · ArgumentException

Can not be Guid.Empty

Error message

Can not be Guid.Empty

What it means

Thrown by EditorConnection.Send(messageId, data, playerId) when messageId is Guid.Empty. Same invariant as Register: every sent message must carry a valid identifier so the player can route it.

Source

Thrown at Editor/Mono/Networking/PlayerConnection/EditorConnection.cs:156

        {
            m_PlayerEditorConnectionEvents.disconnectionEvent.AddPersistentListener(callback, UnityEventCallState.EditorAndRuntime);
        }

        public void UnregisterConnection(UnityAction<int> callback)
        {
            m_PlayerEditorConnectionEvents.connectionEvent.RemovePersistentListener((UnityEngine.Object)callback.Target, callback.Method);
        }

        public void UnregisterDisconnection(UnityAction<int> callback)
        {
            m_PlayerEditorConnectionEvents.disconnectionEvent.RemovePersistentListener((UnityEngine.Object)callback.Target, callback.Method);
        }

        public void Send(Guid messageId, byte[] data, int playerId)
        {
            if (messageId == Guid.Empty)
            {
                throw new ArgumentException("Can not be Guid.Empty", "messageId");
            }

            GetEditorConnectionNativeApi().SendMessage(messageId, data, playerId);
        }

        public void Send(Guid messageId, byte[] data)
        {
            Send(messageId, data, 0);
        }

        public bool TrySend(Guid messageId, byte[] data, int playerId)
        {
            if (messageId == Guid.Empty)
            {
                throw new ArgumentException("Can not be Guid.Empty", "messageId");
            }

            return GetEditorConnectionNativeApi().TrySendMessage(messageId, data, playerId);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Use the same non-empty message Guid used at registration time.
2. Guard with a check or use TrySend which also validates (and returns false rather than throwing only on the native side).
3. Centralize message IDs in a shared constants class.

Example fix

// before
connection.Send(Guid.Empty, bytes, playerId);
// after
connection.Send(k_MsgId, bytes, playerId);

if (messageId != Guid.Empty) connection.Send(messageId, data, playerId);

static bool IsValidMessageId(Guid id) => id != Guid.Empty;

When it happens

Trigger: Calling Send with a default/uninitialized Guid, or a messageId variable that was never set.

Common situations: Sending before subscribing to a known message ID; hardcoded empty Guid in test code; message-ID constant refactored away.

Related errors

• Cant be Guid.Empty
• Cannot add source dependency on empty GUID.
• Cannot add artifact dependency on empty GUID.
• Platform GUID {platformGuid} is not a valid Unity build plat
• Couldn't locate scene asset at path {scenePath}

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/5359af80903515c9. Report an issue: GitHub.