Optional EdiValue segments in segment group generate empty lines

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Hello! I have an issue with serializer when defining segments in segment groups like this:
```csharp
[EdiSegmentGroup(.....)]
public class SG
{
...

[EdiValue("X(100)", Path = "FTX/0")]
public string Aaa { get; set; }

public LOC Bbb { get; set; }

...
}
```
Both properties are nulls (they are optional) and they must not be in the EDI document, but I get line `FTX+'` instead. This can be fixed by moving `Aaa` to separate segment class similar to `Bbb`, but it's just excess code in my case. I want to keep those optional single-parameter segments in segment group class.
Is this by design?

Start by reproducing the serializer behavior with a segment group containing nullable Aaa and Bbb properties, as shown in the issue. Trace the segment-group serialization entry point and compare single-parameter EdiValue handling with the LOC property; done means optional null segments are omitted rather than producing an empty FTX line.

Written by the indexing model from the issue text.