NullReferenceException when triggering event from another class

Question

I get null on my event , and Just can get why . this is my code (shortly)

Here I subscribe to the event

class Form1
{       
public Form1()
{

InitializeComponent();

_domainEventHandler = new cEventHandler();            
_domainEventHandler.OnPrintToScreen +=new PrintToScreen_EventHandler(OnDataToPrint);   

}
//...
}

in main Form I initialize cEventHandler class and subscribe to OnPrintToScreen event , this is event fires whenever I want to print to screen ,

namespace DomainLayer
{
    public delegate void PrintToScreen_EventHandler(object source, string data, string Location);
    /// <summary>
    /// class to handle all events 
    /// </summary>
    public class cEventHandler
    {
        /// <summary>
        /// event to send things back to GUI
        /// </summary>
        public static ScriptingSerial _infrastructureSerialAgent = new ScriptingSerial();

        public cEventHandler()
        {
            _infrastructureSerialAgent.onDataInput += new SerialDataInput_EventHandler(OnDataInput);

        }

        public void OnDataInput(object source , string data , string Location)
        {
            //print to screen
            OnPrintToScreen(this, data, Location);
        }
    }
}

Here I fire It

namespace InfraStructure
{
    public delegate void SerialDataInput_EventHandler(object source , string data , string Location);

    //send command
    //wait for a return line
    public class ScriptingSerial
    {

        public event SerialDataInput_EventHandler onDataInput;
        public ScriptingSerial(/**bla bla**/)
        {
                 //declare stuff
        serialPort.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(port_DataReceived);

        }

        internal void port_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            string serialInputData = serialPort.ReadExisting();
            BufferLog.Add(serialInputData);
            if (onDataInput != null)
            {
                onDataInput(this, serialInputData, "Terminal");
            }

        }

    }

my problem is with the onDataInput event , I dont understand what am I missing :(

this question is not a duplicate because it tackles a more complicated scenario