To return null or throw an exception? :/

Invoke.cs

	public class ValidationMethods
	{
		private IDictionary<object, Func<object, object, Boolean>> _functionTable;

		public IDictionary<object, Func<object, object, Boolean>> FunctionTable
		{
			get
			{
				return _functionTable
				       ?? (_functionTable = new Dictionary<object, Func<object, object, bool>>());
			}
		}

		/// <summary>
		/// Invoke a function previously registered by its token value.
		/// </summary>
		/// <param name="token">Object token function is mapped to.</param>
		/// <param name="arg1">First argument to function</param>
		/// <param name="arg2">Second argument to function</param>
		/// <returns>Nullable{bool}, true or false for result of function, null for an invalid token</returns>
		public bool? Invoke(object token, object arg1, object arg2)
		{
			Func<object, object, Boolean> function;

			FunctionTable.TryGetValue(token, out function);

			if (function != null)
				return function.Invoke(arg1, arg2);

			// call failed
			// throw new Exception("Function not present in mapping table, check function name.");
			return null;
		}

		public void AddMethod(Func<object, object, Boolean> function, object token)
		{
			FunctionTable.Add(token, function);
		}

		public void RemoveMethod(object token)
		{
			FunctionTable.Remove(token);
		}
	}