Deserialization of an empty list (with empty XML tag) results in null

[MarekBak]

Used version:

    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>2.12.2</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.dataformat</groupId>
      <artifactId>jackson-dataformat-xml</artifactId>
      <version>2.12.2</version>
    </dependency>

I'm still observing the same behaviour as in #124 At least with that version it is alwas one null element. With others it varies on class nesting.

@JsonAutoDetect(fieldVisibility=JsonAutoDetect.Visibility.ANY, getterVisibility=JsonAutoDetect.Visibility.NONE,
        setterVisibility=JsonAutoDetect.Visibility.NONE, creatorVisibility=JsonAutoDetect.Visibility.NONE)
@JsonIgnoreProperties(ignoreUnknown = true)
public class StreamingProxyChannel {
    @JacksonXmlProperty(localName = "streamingProxyChannelId")
    private String streamingProxyChannelId;

    public String getStreamingProxyChannelId() {
        return streamingProxyChannelId;
    }

    public void setStreamingProxyChannelId(String streamingProxyChannelId) {
        this.streamingProxyChannelId = streamingProxyChannelId;
    }
}


@JsonAutoDetect(fieldVisibility=JsonAutoDetect.Visibility.ANY, getterVisibility=JsonAutoDetect.Visibility.NONE,
        setterVisibility=JsonAutoDetect.Visibility.NONE, creatorVisibility=JsonAutoDetect.Visibility.NONE)
@JacksonXmlRootElement(localName = "InputProxyChannelStatus")
@JsonIgnoreProperties(ignoreUnknown = true)
public class InputProxyChannelStatus {
    @JacksonXmlProperty(localName = "id")
    private String id;

    @JacksonXmlProperty(localName = "streamingProxyChannelIdList")
    @JacksonXmlElementWrapper(useWrapping = false)
    private List<StreamingProxyChannel> streamingProxyChannelIdList;
	
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }
	
    public List<StreamingProxyChannel> getStreamingProxyChannelIdList() {
        return streamingProxyChannelIdList;
    }

    public void setStreamingProxyChannelIdList(List<StreamingProxyChannel> streamingProxyChannelIdList) {
        this.streamingProxyChannelIdList = streamingProxyChannelIdList;
    }
}


public class ModelTest {
    private final static XmlMapper xmlMapper = new XmlMapper();

    @Test
    public void inputProxyChannelStatusTest() throws IOException {
        String input = "<InputProxyChannelStatus>\n" +
                "<id>2</id>\n" +
                "<streamingProxyChannelIdList>\n" +
                "</streamingProxyChannelIdList>\n" +
                "</InputProxyChannelStatus>";
        InputProxyChannelStatus inputProxyChannelStatus = xmlMapper.readValue(input, InputProxyChannelStatus.class);
        Assert.assertEquals("List should be empty", 0, inputProxyChannelStatus.getStreamingProxyChannelIdList().size());
    }
}

[cowtowncoder]

Ok, I hope to a have a look at this in near future; it does sound like a bug from your description.
Thank you for including version information as well: 2.12 does have a lot of List handling fixes.

[cowtowncoder]

So the situation is a bit different than #124 since you are indicating that list value should be "unwrapped".
Because of that, this entry:

    <streamingProxyChannelIdList>
    </streamingProxyChannelIdList>

is used to construct an instance of streamingProxyChannelId, which is valid (just happens to be missing <streamingProxyChannelId> element.

Now, using useWrapping = true should work but I can see an error for that and will see why that occurs: I don't think that should fail (it should produce an empty List).

[cowtowncoder]

I think that combination of #460 and use of wrapped-style explain the issue here; closing.