Check the in_TransactionItem whether value is passing or not
if it is argument pass the value while invoking
@AminaMD NullReferenceException this exception occurs when you are trying to display variable but that variable is having null values.
Example: var a;
Message Box (a.Tostring);
If you are trying to display a value in message box but with out using this variable in the input dialog box NullReferenceException occurs