Add tests for nil SendError MessageID and Msg

These tests ensure that accessing MessageID and Msg methods on a nil SendError pointer returns the expected values (empty string and nil respectively). This helps in validating the error handling logic and avoiding potential nil pointer dereference issues.

senderror_test.go

@@ -108,6 +108,13 @@ func TestSendError_MessageID(t *testing.T) {
 	}
 }
 
+func TestSendError_MessageIDNil(t *testing.T) {
+	var se *SendError
+	if se.MessageID() != "" {
+		t.Error("expected empty string on nil-senderror")
+	}
+}
+
 func TestSendError_Msg(t *testing.T) {
 	var se *SendError
 	err := returnSendError(ErrAmbiguous, false)
@@ -131,6 +138,13 @@ func TestSendError_Msg(t *testing.T) {
 	}
 }
 
+func TestSendError_MsgNil(t *testing.T) {
+	var se *SendError
+	if se.Msg() != nil {
+		t.Error("expected nil on nil-senderror")
+	}
+}
+
 // returnSendError is a helper method to retunr a SendError with a specific reason
 func returnSendError(r SendErrReason, t bool) error {
 	message := NewMsg()