Unity, camera main null? Can somebody tell me where is my mistake?

<pre>        private void DrawPlayers()
        {
            try
            {
                foreach (Player player in _players.Where(plr => plr != null))
                {
                    if (player == null)
                    {
                        File.WriteAllText("greske.txt", "Here we go with player null error.");
                        return;
                    }

                    if (player.Transform == null)
                    {
                        File.WriteAllText("greske.txt", "Player.Transform is null error");
                        return;
                    }
                    if (Camera.main == null)
                    {
                        File.WriteAllText("greske.txt", "Camera.main is null error");
                        return;
                    }

                    float distanceToObject = Vector3.Distance(Camera.main.transform.position, player.Transform.position);
                    Vector3 playerBoundingVector = new Vector3(Camera.main.WorldToScreenPoint(player.Transform.position).x, Camera.main.WorldToScreenPoint(player.Transform.position).y);

                    if (distanceToObject <= _maxDrawingDistance && playerBoundingVector.z > 0.01 && playerBoundingVector.x > -5 && playerBoundingVector.y > -5 && playerBoundingVector.x < 1920 && playerBoundingVector.y < 1080)
                    {
                        var playerHeadVector = new Vector3(
                            Camera.main.WorldToScreenPoint(player.PlayerBones.Head.position).x,
                            Camera.main.WorldToScreenPoint(player.PlayerBones.Head.position).y,
                            Camera.main.WorldToScreenPoint(player.PlayerBones.Head.position).z);

                        float boxVectorX = Camera.main.WorldToScreenPoint(player.Transform.position).x;
                        float boxVectorY = Camera.main.WorldToScreenPoint(player.PlayerBones.Head.position).y + 10f;
                        float boxHeight = Math.Abs(Camera.main.WorldToScreenPoint(player.PlayerBones.Head.position).y - Camera.main.WorldToScreenPoint(player.Transform.position).y) + 10f;
                        float boxWidth = boxHeight * 0.65f;

                        Color guiBackup = GUI.color;
                        var playerColor = GetPlayerColor(player.Side);
                        var isAi = player.Profile.Info.RegistrationDate <= 0;
                        var deadcolor = player.HealthController.IsAlive ? playerColor : Color.gray;

                        GUI.color = deadcolor;
                        GuiHelper.DrawBox(boxVectorX - boxWidth / 2f, (float)Screen.height - boxVectorY, boxWidth, boxHeight, deadcolor);
                        GuiHelper.DrawLine(new Vector2(playerHeadVector.x - 2f, (float)Screen.height - playerHeadVector.y), new Vector2(playerHeadVector.x + 2f, (float)Screen.height - playerHeadVector.y), deadcolor);
                        GuiHelper.DrawLine(new Vector2(playerHeadVector.x, (float)Screen.height - playerHeadVector.y - 2f), new Vector2(playerHeadVector.x, (float)Screen.height - playerHeadVector.y + 2f), deadcolor);


                        var playerName = isAi ? "[BOT]" : player.Profile.Info.Nickname;
                        string playerDisplayName = player.HealthController.IsAlive ? playerName : playerName + " [MRTAV]";
                        string playerText = $"{playerDisplayName} [{(int)distanceToObject}]M";

                        var playerTextVector = GUI.skin.GetStyle(playerText).CalcSize(new GUIContent(playerText));
                        GUI.Label(new Rect(playerBoundingVector.x - playerTextVector.x / 2f, (float)Screen.height - boxVectorY - 20f, 300f, 50f), playerText);
                        GUI.color = guiBackup;
                    }
                }
            }
            catch (Exception ex)
            {
                File.WriteAllText("greske.txt", ex.ToString());
            }
        }