how to solved An unhandled exception of type 'System.ArgumentNullException' occurred in mscorlib.dll error

I'm trying to learn reflection in c#, and while learning I'm getting this exception.

'System.ArgumentNullException' occurred in mscorlib.dll error

How do I resolve this error?

class Program
{
    static void Main(string[] args)
    {
        Assembly executingAssembly = Assembly.GetExecutingAssembly();

        Type customerType = executingAssembly.GetType("Reflection.Customer");
        object customerInstance = Activator.CreateInstance(customerType);
        MethodInfo GetFullName = customerType.GetMethod("GetFullName");

        string[] methodParameter = new string[2];
        methodParameter[0] = "Minhaj";
        methodParameter[1] = "Patel";
        string Full_Name = (string)GetFullName.Invoke(customerInstance, methodParameter);
        Console.WriteLine("Full Name = {0}", Full_Name);
        Console.ReadKey();

    }
}

Customer Class code

class Customer
{
    public string GetFullName(string First_Name, string Last_Name)
    {
        return First_Name + " " + Last_Name;

    }
}

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