Generate a ACK bases on a HL7 message with MSH.2 = ^~&

According to the documentation on some sites like HL7 v2.5.1 - MSH.2 - Encoding Characters, the recommended value for MSH.2 is ^~\&, but it is possible to set ^~& (HL7 MSH (Message Header))

There is a case where we should allow a message with the value ^~&, but when the ACK is trying to be generated, the follow exception happens

Exception: “Failed to validate the message with error - MSH.9 not available”

This is the test to reproduce this issue:

   [TestMethod]
    public void GenerateAckTest()
    {
        var sampleMessage = @"MSH|^~&|EPIC||||20191107134803|ALEVIB01|ORM^O01|23|T|2.3|||||||||||";
        sampleMessage = $"{sampleMessage}\nPID|1||MRN_123^^^IDX^MRN||Smith F S R E T^John||19600101|M";

        var message = new Message(sampleMessage);
        message.ParseMessage();
        var ack = message.GetACK();

        var ACK_MSH_2 = ack.GetValue("MSH.2");
        var MSG_MSH_2 = message.GetValue("MSH.2");

        Assert.AreEqual(ACK_MSH_2, "^~&");
        Assert.AreEqual(MSG_MSH_2, "^~&");
    }

[jaime-olivares]

This change it is already published in nuget version 2.36

[jaime-olivares]

I am able to reproduce the issue. Analysis in progress…