Unity-Technologies/UnityCsReference · error · ArgumentException

messageId must not be empty

Error message

messageId must not be empty

What it means

Thrown by EditorConnectionInternal.IPlayerEditorConnectionNative.SendMessage when the messageId Guid equals Guid.Empty. The message id is the routing key for editor↔player network messages; an empty Guid cannot be serialized as a valid message tag (it is formatted as 'N' and sent native-side). ArgumentException with the parameter name flags misuse of the API contract.

Source

Thrown at Editor/Mono/EditorConnectionInternal.bindings.cs:27

namespace UnityEditor
{
    [NativeHeader("Runtime/Network/PlayerCommunicator/GeneralConnection.h")]
    enum GeneralConnectionSendMode
    {
        NoBlocking,
        AllowBlocking
    }

    [StaticAccessor("EditorConnection::Get()", StaticAccessorType.Dot)]
    [NativeHeader("Runtime/Network/PlayerCommunicator/EditorConnection.h")]
    [NativeHeader("Runtime/Network/PlayerCommunicator/ManagedProxy/EditorConnectionManaged.h")]
    internal class EditorConnectionInternal : IPlayerEditorConnectionNative
    {
        void IPlayerEditorConnectionNative.SendMessage(Guid messageId, byte[] data, int playerId)
        {
            if (messageId == Guid.Empty)
            {
                throw new ArgumentException(nameof(messageId) + " must not be empty");
            }
            SendMessage(messageId.ToString("N"), data, playerId);
        }

        bool IPlayerEditorConnectionNative.TrySendMessage(Guid messageId, byte[] data, int playerId)
        {
            if (messageId == Guid.Empty)
            {
                throw new ArgumentException(nameof(messageId) + " must not be empty");
            }
            return TrySendMessage(messageId.ToString("N"), data, playerId);
        }

        void IPlayerEditorConnectionNative.Poll()
        {
            PollInternal();
        }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Assign a real Guid to every message id, preferably via Guid.NewGuid() at authoring time and stored as a constant.
2. Guard before sending: if (messageId == Guid.Empty) return; or log and skip.
3. Audit all message-id declarations for `new Guid()` / `default(Guid)` / Guid.Parse on untrusted input.

Example fix

// before
static readonly Guid kMsg = new Guid();
connection.Send(kMsg, bytes);
// after
static readonly Guid kMsg = new Guid("d3b1f8a2-....-...."); // generated, non-empty
connection.Send(kMsg, bytes);

if (messageId == Guid.Empty) throw new ArgumentException("messageId must be non-empty");
connection.Send(messageId, data);

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

When it happens

Trigger: Calling PlayerConnection / EditorConnection.Send(messageId, data) where messageId is Guid.Empty — typically because a Guid field was never assigned (default value) or was loaded from an empty string via Guid.Parse("").

Common situations: A message-type Guid declared as `static readonly Guid kMsg = new Guid();` (defaults to Empty) instead of a generated value; deserializing a message id from config that was blank; copy-paste leaving the Guid unassigned.

Related errors

• Check the connected players list instead
• Must be greater than zero.
• clips
• Must not be empty.
• container

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/b648fa16abbc0450. Report an issue: GitHub.