null values are removed from list

[bj0]

If you serialize a list of nullable objects, the objects set to null are removed from the list:

var obj = new string[] { "one", null, "three", null, "four" };
var tw = new StringWriter();
(new Serializer()).Serialize(tw, obj);
Console.WriteLine(tw.ToString());

returns

- one
- three
- four

Instead, it should use the "null" value from the yaml spec, section 10.2.1.1. Null

- one
- null
- three
- null
- four

Otherwise lengths and positions of array elements can be lost.

[roji]

@aaubry:

Reproduced in unit testing here: roji@7642951

The problem is that when EmitDefaults is false (the default), the DefaultExclusiveObjectGraphVisitor skips all nulls/defaults, regardless of whether they're in a collection or not.

I think it is difficult to resolve this issue with the current design, where default exclusion happens in a visitor (which has no context of where it is in the object graph. In roji@9fe1e94, I moved the default exclusion logic from the visitor to the TraversalStrategy, where much more context is available. I think that would be the correct solution to this bug as well.

The other alternative is to track graph context information inside the visitor (based on calls to VisitSequenceStart, VisitMappingStart), but that seems needless and complicated to me...

If you're OK with moving the default exclusion logic to the TraversalStrategy, I can submit a pull request fixing this.

[aaubry]

Actually this one was a simple bug in the visitor. It has been fixed on commit e9019d5.

[roji]

Oops, missed that...